Network Working Group                                           E. Rosen
Request for Comments: 4364                           Cisco Systems, Inc.
Obsoletes: 2547                                               Y. Rekhter
Category: Standards Track                         Juniper Networks, Inc.
                                                           February 2006
Network Working Group                                           E. Rosen
Request for Comments: 4364                           Cisco Systems, Inc.
Obsoletes: 2547                                               Y. Rekhter
Category: Standards Track                         Juniper Networks, Inc.
                                                           February 2006

BGP/MPLS IP Virtual Private Networks (VPNs)


Status of This Memo


This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.

本文件规定了互联网社区的互联网标准跟踪协议,并要求进行讨论和提出改进建议。有关本协议的标准化状态和状态,请参考当前版本的“互联网官方协议标准”(STD 1)。本备忘录的分发不受限制。

Copyright Notice


Copyright (C) The Internet Society (2006).




This document describes a method by which a Service Provider may use an IP backbone to provide IP Virtual Private Networks (VPNs) for its customers. This method uses a "peer model", in which the customers' edge routers (CE routers) send their routes to the Service Provider's edge routers (PE routers); there is no "overlay" visible to the customer's routing algorithm, and CE routers at different sites do not peer with each other. Data packets are tunneled through the backbone, so that the core routers do not need to know the VPN routes.


This document obsoletes RFC 2547.

本文件废除RFC 2547。

Table of Contents


   1. Introduction ....................................................3
      1.1. Virtual Private Networks ...................................4
      1.2. Customer Edge and Provider Edge ............................5
      1.3. VPNs with Overlapping Address Spaces .......................6
      1.4. VPNs with Different Routes to the Same System ..............7
      1.5. SP Backbone Routers ........................................7
      1.6. Security ...................................................8
   2. Sites and CEs ...................................................8
   3. VRFs: Multiple Forwarding Tables in PEs .........................9
      3.1. VRFs and Attachment Circuits ...............................9
      3.2. Associating IP Packets with VRFs ..........................10
      3.3. Populating the VRFs .......................................11
   4. VPN Route Distribution via BGP .................................12
      4.1. The VPN-IPv4 Address Family ...............................13
      4.2. Encoding of Route Distinguishers ..........................14
      4.3. Controlling Route Distribution ............................15
           4.3.1. The Route Target Attribute .........................15
           4.3.2. Route Distribution Among PEs by BGP ................17
           4.3.3. Use of Route Reflectors ............................20
           4.3.4. How VPN-IPv4 NLRI Is Carried in BGP ................22
           4.3.5. Building VPNs Using Route Targets ..................23
           4.3.6. Route Distribution Among VRFs in a Single PE .......23
   5. Forwarding .....................................................23
   6. Maintaining Proper Isolation of VPNs ...........................26
   7. How PEs Learn Routes from CEs ..................................27
   8. How CEs Learn Routes from PEs ..................................30
   9. Carriers' Carriers .............................................30
   10. Multi-AS Backbones ............................................32
   11. Accessing the Internet from a VPN .............................34
   12. Management VPNs ...............................................36
   13. Security Considerations .......................................37
      13.1. Data Plane ...............................................37
      13.2. Control Plane ............................................39
      13.3. Security of P and PE Devices .............................39
   14. Quality of Service ............................................39
   15. Scalability ...................................................40
   16. IANA Considerations ...........................................40
   17. Acknowledgements ..............................................41
   18. Contributors ..................................................41
   19. Normative References ..........................................44
   20. Informative References ........................................45
   1. Introduction ....................................................3
      1.1. Virtual Private Networks ...................................4
      1.2. Customer Edge and Provider Edge ............................5
      1.3. VPNs with Overlapping Address Spaces .......................6
      1.4. VPNs with Different Routes to the Same System ..............7
      1.5. SP Backbone Routers ........................................7
      1.6. Security ...................................................8
   2. Sites and CEs ...................................................8
   3. VRFs: Multiple Forwarding Tables in PEs .........................9
      3.1. VRFs and Attachment Circuits ...............................9
      3.2. Associating IP Packets with VRFs ..........................10
      3.3. Populating the VRFs .......................................11
   4. VPN Route Distribution via BGP .................................12
      4.1. The VPN-IPv4 Address Family ...............................13
      4.2. Encoding of Route Distinguishers ..........................14
      4.3. Controlling Route Distribution ............................15
           4.3.1. The Route Target Attribute .........................15
           4.3.2. Route Distribution Among PEs by BGP ................17
           4.3.3. Use of Route Reflectors ............................20
           4.3.4. How VPN-IPv4 NLRI Is Carried in BGP ................22
           4.3.5. Building VPNs Using Route Targets ..................23
           4.3.6. Route Distribution Among VRFs in a Single PE .......23
   5. Forwarding .....................................................23
   6. Maintaining Proper Isolation of VPNs ...........................26
   7. How PEs Learn Routes from CEs ..................................27
   8. How CEs Learn Routes from PEs ..................................30
   9. Carriers' Carriers .............................................30
   10. Multi-AS Backbones ............................................32
   11. Accessing the Internet from a VPN .............................34
   12. Management VPNs ...............................................36
   13. Security Considerations .......................................37
      13.1. Data Plane ...............................................37
      13.2. Control Plane ............................................39
      13.3. Security of P and PE Devices .............................39
   14. Quality of Service ............................................39
   15. Scalability ...................................................40
   16. IANA Considerations ...........................................40
   17. Acknowledgements ..............................................41
   18. Contributors ..................................................41
   19. Normative References ..........................................44
   20. Informative References ........................................45
1. Introduction
1. 介绍

This document describes a method by which a Service Provider may use an IP backbone to provide IP Virtual Private Networks (VPNs) for its customers. This method uses a "peer model", in which the customers' edge routers (CE routers) send their routes to the Service Provider's edge routers (PE routers). Border Gateway Protocol (BGP) [BGP, BGP-MP] is then used by the Service Provider to exchange the routes of a particular VPN among the PE routers that are attached to that VPN. This is done in a way that ensures that routes from different VPNs remain distinct and separate, even if two VPNs have an overlapping address space. The PE routers distribute, to the CE routers in a particular VPN, the routes from other the CE routers in that VPN. The CE routers do not peer with each other, hence there is no "overlay" visible to the VPN's routing algorithm. The term "IP" in "IP VPN" is used to indicate that the PE receives IP datagrams from the CE, examines their IP headers, and routes them accordingly.

本文档描述了一种方法,通过该方法,服务提供商可以使用IP主干为其客户提供IP虚拟专用网络(VPN)。该方法使用“对等模型”,其中客户的边缘路由器(CE路由器)将其路由发送到服务提供商的边缘路由器(PE路由器)。然后,服务提供商使用边界网关协议(BGP)[BGP,BGP-MP]在连接到该VPN的PE路由器之间交换特定VPN的路由。这样做可以确保来自不同VPN的路由保持不同和分离,即使两个VPN有重叠的地址空间。PE路由器将来自该VPN中其他CE路由器的路由分配给特定VPN中的CE路由器。CE路由器彼此不对等,因此VPN的路由算法看不到“覆盖”。“IP VPN”中的术语“IP”用于指示PE从CE接收IP数据报,检查其IP报头,并相应地路由它们。

Each route within a VPN is assigned a Multiprotocol Label Switching (MPLS) [MPLS-ARCH, MPLS-BGP, MPLS-ENCAPS] label; when BGP distributes a VPN route, it also distributes an MPLS label for that route. Before a customer data packet travels across the Service Provider's backbone, it is encapsulated with the MPLS label that corresponds, in the customer's VPN, to the route that is the best match to the packet's destination address. This MPLS packet is further encapsulated (e.g., with another MPLS label or with an IP or Generic Routing Encapsulation (GRE) tunnel header [MPLS-in-IP-GRE]) so that it gets tunneled across the backbone to the proper PE router. Thus, the backbone core routers do not need to know the VPN routes.

VPN内的每条路由都被分配一个多协议标签交换(MPLS)[MPLS-ARCH、MPLS-BGP、MPLS-ENCAPS]标签;当BGP分发VPN路由时,它还为该路由分发MPLS标签。在客户数据包穿越服务提供商的主干网之前,它被封装为MPLS标签,该标签在客户的VPN中对应于与数据包的目的地地址最匹配的路由。该MPLS数据包被进一步封装(例如,使用另一个MPLS标签或IP或通用路由封装(GRE)隧道头[IP GRE中的MPLS]),以便它通过主干隧道传输到适当的PE路由器。因此,骨干核心路由器不需要知道VPN路由。

The primary goal of this method is to support the case in which a client obtains IP backbone services from a Service Provider or Service Providers with which it maintains contractual relationships. The client may be an enterprise, a group of enterprises that need an extranet, an Internet Service Provider, an application service provider, another VPN Service Provider that uses this same method to offer VPNs to clients of its own, etc. The method makes it very simple for the client to use the backbone services. It is also very scalable and flexible for the Service Provider, and allows the Service Provider to add value.


1.1. Virtual Private Networks
1.1. 虚拟专用网络

Consider a set of "sites" that are attached to a common network that we call "the backbone". Now apply some policy to create a number of subsets of that set, and impose the following rule: two sites may have IP interconnectivity over that backbone only if at least one of these subsets contains them both.


These subsets are Virtual Private Networks (VPNs). Two sites have IP connectivity over the common backbone only if there is some VPN that contains them both. Two sites that have no VPN in common have no connectivity over that backbone.


If all the sites in a VPN are owned by the same enterprise, the VPN may be thought of as a corporate "intranet". If the various sites in a VPN are owned by different enterprises, the VPN may be thought of as an "extranet". A site can be in more than one VPN; e.g., in an intranet and in several extranets. In general, when we use the term "VPN" we will not be distinguishing between intranets and extranets.

如果VPN中的所有站点都属于同一个企业,则VPN可以被视为企业“内部网”。如果VPN中的各个站点由不同的企业拥有,则VPN可被视为“外联网”。一个站点可以位于多个VPN中;e、 例如,在一个内部网和几个外部网中。一般来说,当我们使用术语“VPN”时,我们不会区分内部网和外部网。

We refer to the owners of the sites as the "customers". We refer to the owners/operators of the backbone as the "Service Providers" (SPs). The customers obtain "VPN service" from the SPs.


A customer may be a single enterprise, a set of enterprises, an Internet Service Provider, an Application Service Provider, another SP that offers the same kind of VPN service to its own customers, etc.


The policies that determine whether a particular collection of sites is a VPN are the policies of the customers. Some customers will want the implementation of these policies to be entirely the responsibility of the SP. Other customers may want to share with the SP the responsibility for implementing these policies. This document specifies mechanisms that can be used to implement these policies. The mechanisms we describe are general enough to allow these policies to be implemented either by the SP alone or by a VPN customer together with the SP. Most of the discussion is focused on the former case, however.


The mechanisms discussed in this document allow the implementation of a wide range of policies. For example, within a given VPN, one can allow every site to have a direct route to every other site ("full mesh"). Alternatively, one can force traffic between certain pairs of sites to be routed via a third site. This can be useful, e.g., if it is desired that traffic between a pair of sites be passed through a firewall, and the firewall is located at the third site.


In this document, we restrict our discussion to the case in which the customer is explicitly purchasing VPN service from an SP, or from a set of SPs that have agreed to cooperate to provide the VPN service. That is, the customer is not merely purchasing internet access from an SP, and the VPN traffic does not pass through a random collection of interconnected SP networks.


We also restrict our discussion to the case in which the backbone provides an IP service to the customer, rather than, e.g., a layer 2 service such as Frame Relay, Asynchronous Transfer Mode (ATM), ethernet, High Level Data Link Control (HDLC), or Point-to-Point Protocol (PPP). The customer may attach to the backbone via one of these (or other) layer 2 services, but the layer 2 service is terminated at the "edge" of the backbone, where the customer's IP datagrams are removed from any layer 2 encapsulation.


In the rest of this introduction, we specify some properties that VPNs should have. The remainder of this document specifies a set of mechanisms that can be deployed to provide a VPN model that has all these properties. This section also introduces some of the technical terminology used in the remainder of the document.


1.2. Customer Edge and Provider Edge
1.2. 客户优势和提供商优势

Routers can be attached to each other, or to end systems, in a variety of different ways: PPP connections, ATM Virtual Circuits (VCs), Frame Relay VCs, ethernet interfaces, Virtual Local Area Networks (VLANs) on ethernet interfaces, GRE tunnels, Layer 2 Tunneling Protocol (L2TP) tunnels, IPsec tunnels, etc. We will use the term "attachment circuit" to refer generally to some such means of attaching to a router. An attachment circuit may be the sort of connection that is usually thought of as a "data link", or it may be a tunnel of some sort; what matters is that it be possible for two devices to be network layer peers over the attachment circuit.


Each VPN site must contain one or more Customer Edge (CE) devices. Each CE device is attached, via some sort of attachment circuit, to one or more Provider Edge (PE) routers.


Routers in the SP's network that do not attach to CE devices are known as "P routers".


CE devices can be hosts or routers. In a typical case, a site contains one or more routers, some of which are attached to PE routers. The site routers that attach to the PE routers would then be the CE devices, or "CE routers". However, there is nothing to prevent a non-routing host from attaching directly to a PE router, in which case the host would be a CE device.


Sometimes, what is physically attached to a PE router is a layer 2 switch. In this case, we do NOT say that the layer 2 switch is a CE device. Rather, the CE devices are the hosts and routers that communicate with the PE router through the layer 2 switch; the layer 2 infrastructure is transparent. If the layer 2 infrastructure provides a multipoint service, then multiple CE devices can be attached to the PE router over the same attachment circuit.


CE devices are logically part of a customer's VPN. PE and P routers are logically part of the SP's network.


The attachment circuit over which a packet travels when going from CE to PE is known as that packet's "ingress attachment circuit", and the PE as the packet's "ingress PE". The attachment circuit over which a packet travels when going from PE to CE is known as that packet's "egress attachment circuit", and the PE as the packet's "egress PE".


We will say that a PE router is attached to a particular VPN if it is attached to a CE device that is in a site of that VPN. Similarly, we will say that a PE router is attached to a particular site if it is attached to a CE device that is in that site.


When the CE device is a router, it is a routing peer of the PE(s) to which it is attached, but it is NOT a routing peer of CE routers at other sites. Routers at different sites do not directly exchange routing information with each other; in fact, they do not even need to know of each other at all. As a consequence, the customer has no backbone or "virtual backbone" to manage, and does not have to deal with any inter-site routing issues. In other words, in the scheme described in this document, a VPN is NOT an "overlay" on top of the SP's network.


With respect to the management of the edge devices, clear administrative boundaries are maintained between the SP and its customers. Customers are not required to access the PE or P routers for management purposes, nor is the SP required to access the CE devices for management purposes.


1.3. VPNs with Overlapping Address Spaces
1.3. 具有重叠地址空间的VPN

If two VPNs have no sites in common, then they may have overlapping address spaces. That is, a given address might be used in VPN V1 as the address of system S1, but in VPN V2 as the address of a completely different system S2. This is a common situation when the VPNs each use an RFC 1918 private address space. Of course, within each VPN, each address must be unambiguous.

如果两个VPN没有共同的站点,则它们可能有重叠的地址空间。也就是说,给定的地址可能在VPN V1中用作系统S1的地址,但在VPN V2中用作完全不同的系统S2的地址。当VPN各自使用RFC 1918专用地址空间时,这是一种常见情况。当然,在每个VPN中,每个地址都必须是明确的。

Even two VPNs that do have sites in common may have overlapping address spaces, as long as there is no need for any communication between systems with such addresses and systems in the common sites.


1.4. VPNs with Different Routes to the Same System
1.4. 不同路由到同一系统的VPN

Although a site may be in multiple VPNs, it is not necessarily the case that the route to a given system at that site should be the same in all the VPNs. Suppose, for example, we have an intranet consisting of sites A, B, and C, and an extranet consisting of A, B, C, and the "foreign" site D. Suppose that at site A there is a server, and we want clients from B, C, or D to be able to use that server. Suppose also that at site B there is a firewall. We want all the traffic from site D to the server to pass through the firewall, so that traffic from the extranet can be access controlled. However, we don't want traffic from C to pass through the firewall on the way to the server, since this is intranet traffic.


It is possible to set up two routes to the server. One route, used by sites B and C, takes the traffic directly to site A. The second route, used by site D, takes the traffic instead to the firewall at site B. If the firewall allows the traffic to pass, it then appears to be traffic coming from site B, and follows the route to site A.


1.5. SP Backbone Routers
1.5. SP骨干路由器

The SP's backbone consists of the PE routers, as well as other routers ("P routers") that do not attach to CE devices.


If every router in an SP's backbone had to maintain routing information for all the VPNs supported by the SP, there would be severe scalability problems; the number of sites that could be supported would be limited by the amount of routing information that could be held in a single router. It is important therefore that the routing information about a particular VPN only needs to be present in the PE routers that attach to that VPN. In particular, the P routers do not need to have ANY per-VPN routing information whatsoever. (This condition may need to be relaxed somewhat when multicast routing is considered. This is not considered further in this paper, but is examined in [VPN-MCAST].)


So just as the VPN owners do not have a backbone or "virtual backbone" to administer, the SPs themselves do not have a separate backbone or "virtual backbone" to administer for each VPN. Site-to-site routing in the backbone is optimal (within the constraints of the policies used to form the VPNs) and is not constrained in any way by an artificial "virtual topology" of tunnels.


Section 10 discusses some of the special issues that arise when the backbone spans several Service Providers.


1.6. Security
1.6. 安全

VPNs of the sort being discussed here, even without making use of cryptographic security measures, are intended to provide a level of security equivalent to that obtainable when a layer 2 backbone (e.g., Frame Relay) is used. That is, in the absence of misconfiguration or deliberate interconnection of different VPNs, it is not possible for systems in one VPN to gain access to systems in another VPN. Of course, the methods described herein do not by themselves encrypt the data for privacy, nor do they provide a way to determine whether data has been tampered with en route. If this is desired, cryptographic measures must be applied in addition. (See, e.g., [MPLS/BGP-IPsec].) Security is discussed in more detail in Section 13.

这里讨论的这类VPN,即使不使用加密安全措施,也旨在提供与使用第2层主干(例如帧中继)时可获得的安全级别相当的安全级别。也就是说,在不同VPN没有错误配置或故意互连的情况下,一个VPN中的系统不可能访问另一个VPN中的系统。当然,本文描述的方法本身并不出于隐私目的对数据进行加密,也不提供确定数据是否在途中被篡改的方法。如果需要,还必须应用加密措施。(例如,参见[MPLS/BGP IPsec])第13节将更详细地讨论安全性。

2. Sites and CEs
2. 网站和消费电子产品

From the perspective of a particular backbone network, a set of IP systems may be regarded as a "site" if those systems have mutual IP interconnectivity that doesn't require use of the backbone. In general, a site will consist of a set of systems that are in geographic proximity. However, this is not universally true. If two geographic locations are connected via a leased line, over which Open Shortest Path First (OSPF) protocol [OSPFv2] is running, and if that line is the preferred way of communicating between the two locations, then the two locations can be regarded as a single site, even if each location has its own CE router. (This notion of "site" is topological, rather than geographical. If the leased line goes down, or otherwise ceases to be the preferred route, but the two geographic locations can continue to communicate by using the VPN backbone, then one site has become two.)


A CE device is always regarded as being in a single site (though as we shall see in Section 3.2, a site may consist of multiple "virtual sites"). A site, however, may belong to multiple VPNs.


A PE router may attach to CE devices from any number of different sites, whether those CE devices are in the same or in different VPNs. A CE device may, for robustness, attach to multiple PE routers, of the same or of different service providers. If the CE device is a router, the PE router and the CE router will appear as router adjacencies to each other.


While we speak mostly of "sites" as being the basic unit of interconnection, nothing here prevents a finer degree of granularity in the control of interconnectivity. For example, certain systems at


a site may be members of an intranet as well as members of one or more extranets, while other systems at the same site may be restricted to being members of the intranet only. However, this might require that the site have two attachment circuits to the backbone, one for the intranet and one for the extranet; it might further require that firewall functionality be applied on the extranet attachment circuit.


3. VRFs: Multiple Forwarding Tables in PEs
3. VRFs:PEs中的多个转发表

Each PE router maintains a number of separate forwarding tables. One of the forwarding tables is the "default forwarding table". The others are "VPN Routing and Forwarding tables", or "VRFs".


3.1. VRFs and Attachment Circuits
3.1. VRF和连接电路

Every PE/CE attachment circuit is associated, by configuration, with one or more VRFs. An attachment circuit that is associated with a VRF is known as a "VRF attachment circuit".


In the simplest case and most typical case, a PE/CE attachment circuit is associated with exactly one VRF. When an IP packet is received over a particular attachment circuit, its destination IP address is looked up in the associated VRF. The result of that lookup determines how to route the packet. The VRF used by a packet's ingress PE for routing a particular packet is known as the packet's "ingress VRF". (There is also the notion of a packet's "egress VRF", located at the packet's egress PE; this is discussed in Section 5.)


If an IP packet arrives over an attachment circuit that is not associated with any VRF, the packet's destination address is looked up in the default forwarding table, and the packet is routed accordingly. Packets forwarded according to the default forwarding table include packets from neighboring P or PE routers, as well as packets from customer-facing attachment circuits that have not been associated with VRFs.


Intuitively, one can think of the default forwarding table as containing "public routes", and of the VRFs as containing "private routes". One can similarly think of VRF attachment circuits as being "private", and of non-VRF attachment circuits as being "public".


If a particular VRF attachment circuit connects site S to a PE router, then connectivity from S (via that attachment circuit) can be restricted by controlling the set of routes that gets entered in the corresponding VRF. The set of routes in that VRF should be limited to the set of routes leading to sites that have at least one VPN in


common with S. Then a packet sent from S over a VRF attachment circuit can only be routed by the PE to another site S' if S' is in one of the same VPNs as S. That is, communication (via PE routers) is prevented between any pair of VPN sites that have no VPN in common. Communication between VPN sites and non-VPN sites is prevented by keeping the routes to the VPN sites out of the default forwarding table.


If there are multiple attachment circuits leading from S to one or more PE routers, then there might be multiple VRFs that could be used to route traffic from S. To properly restrict S's connectivity, the same set of routes would have to exist in all the VRFs. Alternatively, one could impose different connectivity restrictions over different attachment circuit from S. In that case, some of the VRFs associated with attachment circuits from S would contain different sets of routes than some of the others.


We allow the case in which a single attachment circuit is associated with a set of VRFs, rather than with a single VRF. This can be useful if it is desired to divide a single VPN into several "sub-VPNs", each with different connectivity restrictions, where some characteristic of the customer packets is used to select from among the sub-VPNs. For simplicity though, we will usually speak of an attachment circuit as being associated with a single VRF.


3.2. Associating IP Packets with VRFs
3.2. 将IP数据包与VRF关联

When a PE router receives a packet from a CE device, it must determine the attachment circuit over which the packet arrived, as this determines in turn the VRF (or set of VRFs) that can be used for forwarding that packet. In general, to determine the attachment circuit over which a packet arrived, a PE router takes note of the physical interface over which the packet arrived, and possibly also takes note of some aspect of the packet's layer 2 header. For example, if a packet's ingress attachment circuit is a Frame Relay VC, the identity of the attachment circuit can be determined from the physical Frame Relay interface over which the packet arrived, together with the Data Link Connection Identifier (DLCI) field in the packet's Frame Relay header.


Although the PE's conclusion that a particular packet arrived on a particular attachment circuit may be partially determined by the packet's layer 2 header, it must be impossible for a customer, by writing the header fields, to fool the SP into thinking that a packet that was received over one attachment circuit really arrived over a different one. In the example above, although the attachment circuit is determined partially by inspection of the DLCI field in the Frame Relay header, this field cannot be set freely by the customer.


Rather, it must be set to a value specified by the SP, or else the packet cannot arrive at the PE router.


In some cases, a particular site may be divided by the customer into several "virtual sites". The SP may designate a particular set of VRFs to be used for routing packets from that site and may allow the customer to set some characteristic of the packet, which is then used for choosing a particular VRF from the set.


For example, each virtual site might be realized as a VLAN. The SP and the customer could agree that on packets arriving from a particular CE, certain VLAN values would be used to identify certain VRFs. Of course, packets from that CE would be discarded by the PE if they carry VLAN tag values that are not in the agreed-upon set. Another way to accomplish this is to use IP source addresses. In this case, the PE uses the IP source address in a packet received from the CE, along with the interface over which the packet is received, to assign the packet to a particular VRF. Again, the customer would only be able to select from among the particular set of VRFs that that customer is allowed to use.


If it is desired to have a particular host be in multiple virtual sites, then that host must determine, for each packet, which virtual site the packet is associated with. It can do this, e.g., by sending packets from different virtual sites on different VLANs, or out different network interfaces.


3.3. Populating the VRFs
3.3. 填充VRF

With what set of routes are the VRFs populated?


As an example, let PE1, PE2, and PE3 be three PE routers, and let CE1, CE2, and CE3 be three CE routers. Suppose that PE1 learns, from CE1, the routes that are reachable at CE1's site. If PE2 and PE3 are attached, respectively, to CE2 and CE3, and there is some VPN V containing CE1, CE2, and CE3, then PE1 uses BGP to distribute to PE2 and PE3 the routes that it has learned from CE1. PE2 and PE3 use these routes to populate the VRFs that they associate, respectively, with the sites of CE2 and CE3. Routes from sites that are not in VPN V do not appear in these VRFs, which means that packets from CE2 or CE3 cannot be sent to sites that are not in VPN V.

例如,假设PE1、PE2和PE3是三个PE路由器,假设CE1、CE2和CE3是三个CE路由器。假设PE1从CE1学习到在CE1的站点上可以到达的路由。如果PE2和PE3分别连接到CE2和CE3,并且有一些VPN V包含CE1、CE2和CE3,那么PE1使用BGP将从CE1学到的路由分发给PE2和PE3。PE2和PE3使用这些路线填充它们分别与CE2和CE3站点关联的VRF。来自不在VPN V中的站点的路由不会出现在这些VRF中,这意味着来自CE2或CE3的数据包无法发送到不在VPN V中的站点。

When we speak of a PE "learning" routes from a CE, we are not presupposing any particular learning technique. The PE may learn routes by means of a dynamic routing algorithm, but it may also "learn" routes by having those routes configured (i.e., static routing). (In this case, to say that the PE "learned" the routes from the CE is perhaps to exercise a bit of poetic license.)


PEs also need to learn, from other PEs, the routes that belong to a given VPN. The procedures to be used for populating the VRFs with the proper sets of routes are specified in Section 4.


If there are multiple attachment circuits leading from a particular PE router to a particular site, they might all be mapped to the same forwarding table. But if policy dictates, they could be mapped to different forwarding tables. For instance, the policy might be that a particular attachment circuit from a site is used only for intranet traffic, while another attachment circuit from that site is used only for extranet traffic. (Perhaps, e.g., the CE attached to the extranet attachment circuit is a firewall, while the CE attached to the intranet attachment circuit is not.) In this case, the two attachment circuits would be associated with different VRFs.


Note that if two attachment circuits are associated with the same VRF, then packets that the PE receives over one of them will be able to reach exactly the same set of destinations as packets that the PE receives over the other. So two attachment circuits cannot be associated with the same VRF unless each CE is in the exact same set of VPNs as is the other.


If an attachment circuit leads to a site which is in multiple VPNs, the attachment circuit may still associated with a single VRF, in which case the VRF will contain routes from the full set of VPNs of which the site is a member.


4. VPN Route Distribution via BGP
4. 基于BGP的VPN路由分配

PE routers use BGP to distribute VPN routes to each other (more accurately, to cause VPN routes to be distributed to each other).


We allow each VPN to have its own address space, which means that a given address may denote different systems in different VPNs. If two routes to the same IP address prefix are actually routes to different systems, it is important to ensure that BGP not treat them as comparable. Otherwise, BGP might choose to install only one of them, making the other system unreachable. Further, we must ensure that POLICY is used to determine which packets get sent on which routes; given that several such routes are installed by BGP, only one such must appear in any particular VRF.


We meet these goals by the use of a new address family, as specified below.


4.1. The VPN-IPv4 Address Family
4.1. VPN-IPv4地址系列

The BGP Multiprotocol Extensions [BGP-MP] allow BGP to carry routes from multiple "address families". We introduce the notion of the "VPN-IPv4 address family". A VPN-IPv4 address is a 12-byte quantity, beginning with an 8-byte Route Distinguisher (RD) and ending with a 4-byte IPv4 address. If several VPNs use the same IPv4 address prefix, the PEs translate these into unique VPN-IPv4 address prefixes. This ensures that if the same address is used in several different VPNs, it is possible for BGP to carry several completely different routes to that address, one for each VPN.


Since VPN-IPv4 addresses and IPv4 addresses are different address families, BGP never treats them as comparable addresses.


An RD is simply a number, and it does not contain any inherent information; it does not identify the origin of the route or the set of VPNs to which the route is to be distributed. The purpose of the RD is solely to allow one to create distinct routes to a common IPv4 address prefix. Other means are used to determine where to redistribute the route (see Section 4.3).


The RD can also be used to create multiple different routes to the very same system. We have already discussed a situation in which the route to a particular server should be different for intranet traffic than for extranet traffic. This can be achieved by creating two different VPN-IPv4 routes that have the same IPv4 part, but different RDs. This allows BGP to install multiple different routes to the same system, and allows policy to be used (see Section 4.3.5) to decide which packets use which route.


The RDs are structured so that every Service Provider can administer its own "numbering space" (i.e., can make its own assignments of RDs), without conflicting with the RD assignments made by any other Service Provider. An RD consists of three fields: a 2-byte type field, an administrator field, and an assigned number field. The value of the type field determines the lengths of the other two fields, as well as the semantics of the administrator field. The administrator field identifies an assigned number authority, and the assigned number field contains a number that has been assigned, by the identified authority, for a particular purpose. For example, one could have an RD whose administrator field contains an Autonomous System number (ASN), and whose (4-byte) number field contains a number assigned by the SP to whom that ASN belongs (having been assigned to that SP by the appropriate authority).


RDs are given this structure in order to ensure that an SP that provides VPN backbone service can always create a unique RD when it


needs to do so. However, the structure is not meaningful to BGP; when BGP compares two such address prefixes, it ignores the structure entirely.


A PE needs to be configured such that routes that lead to a particular CE become associated with a particular RD. The configuration may cause all routes leading to the same CE to be associated with the same RD, or it may cause different routes to be associated with different RDs, even if they lead to the same CE.


4.2. Encoding of Route Distinguishers
4.2. 路由识别器的编码

As stated, a VPN-IPv4 address consists of an 8-byte Route Distinguisher followed by a 4-byte IPv4 address. The RDs are encoded as follows:


- Type Field: 2 bytes - Value Field: 6 bytes

- 类型字段:2字节-值字段:6字节

The interpretation of the Value field depends on the value of the type field. At the present time, three values of the type field are defined: 0, 1, and 2.


- Type 0: The Value field consists of two subfields:

- 类型0:值字段由两个子字段组成:

* Administrator subfield: 2 bytes * Assigned Number subfield: 4 bytes

* 管理员子字段:2字节*分配的编号子字段:4字节

The Administrator subfield must contain an Autonomous System number. If this ASN is from the public ASN space, it must have been assigned by the appropriate authority (use of ASN values from the private ASN space is strongly discouraged). The Assigned Number subfield contains a number from a numbering space that is administered by the enterprise to which the ASN has been assigned by an appropriate authority.

管理员子字段必须包含自治系统编号。如果此ASN来自公共ASN空间,则它必须由适当的机构分配(强烈反对使用来自私有ASN空间的ASN值)。Assigned Number(已分配编号)子字段包含来自编号空间的编号,该编号空间由ASN已由相应机构分配给的企业管理。

- Type 1: The Value field consists of two subfields:

- 类型1:值字段由两个子字段组成:

* Administrator subfield: 4 bytes * Assigned Number subfield: 2 bytes

* 管理员子字段:4字节*分配的编号子字段:2字节

The Administrator subfield must contain an IP address. If this IP address is from the public IP address space, it must have been assigned by an appropriate authority (use of addresses from the private IP address space is strongly discouraged). The Assigned Number subfield contains a number from a numbering space which is administered by the enterprise to which the IP address has been assigned.

管理员子字段必须包含IP地址。如果此IP地址来自公共IP地址空间,则必须由适当的机构分配(强烈建议使用来自私有IP地址空间的地址)。Assigned Number子字段包含来自编号空间的编号,该编号空间由IP地址已分配到的企业管理。

- Type 2: The Value field consists of two subfields:

- 类型2:值字段由两个子字段组成:

* Administrator subfield: 4 bytes * Assigned Number subfield: 2 bytes

* 管理员子字段:4字节*分配的编号子字段:2字节

The Administrator subfield must contain a 4-byte Autonomous System number [BGP-AS4]. If this ASN is from the public ASN space, it must have been assigned by the appropriate authority (use of ASN values from the private ASN space is strongly discouraged). The Assigned Number subfield contains a number from a numbering space which is administered by the enterprise to which the ASN has been assigned by an appropriate authority.

管理员子字段必须包含一个4字节的自治系统编号[BGP-AS4]。如果此ASN来自公共ASN空间,则它必须由适当的机构分配(强烈反对使用来自私有ASN空间的ASN值)。Assigned Number(已分配编号)子字段包含编号空间中的编号,该编号空间由ASN已由相关机构分配给的企业管理。

4.3. Controlling Route Distribution
4.3. 控制路线分布

In this section, we discuss the way in which the distribution of the VPN-IPv4 routes is controlled.


If a PE router is attached to a particular VPN (by being attached to a particular CE in that VPN), it learns some of that VPN's IP routes from the attached CE router. Routes learned from a CE routing peer over a particular attachment circuit may be installed in the VRF associated with that attachment circuit. Exactly which routes are installed in this manner is determined by the way in which the PE learns routes from the CE. In particular, when the PE and CE are routing protocol peers, this is determined by the decision process of the routing protocol; this is discussed in Section 7.


These routes are then converted to VPN-IP4 routes, and "exported" to BGP. If there is more than one route to a particular VPN-IP4 address prefix, BGP chooses the "best" one, using the BGP decision process. That route is then distributed by BGP to the set of other PEs that need to know about it. At these other PEs, BGP will again choose the best route for a particular VPN-IP4 address prefix. Then the chosen VPN-IP4 routes are converted back into IP routes, and "imported" into one or more VRFs. Whether they are actually installed in the VRFs depends on the decision process of the routing method used between the PE and those CEs that are associated with the VRF in question. Finally, any route installed in a VRF may be distributed to the associated CE routers.


4.3.1. The Route Target Attribute
4.3.1. 路由目标属性

Every VRF is associated with one or more Route Target (RT) attributes.


When a VPN-IPv4 route is created (from an IPv4 route that the PE has learned from a CE) by a PE router, it is associated with one or more


Route Target attributes. These are carried in BGP as attributes of the route.


Any route associated with Route Target T must be distributed to every PE router that has a VRF associated with Route Target T. When such a route is received by a PE router, it is eligible to be installed in those of the PE's VRFs that are associated with Route Target T. (Whether it actually gets installed depends upon the outcome of the BGP decision process, and upon the outcome of the decision process of the IGP (i.e., the intra-domain routing protocol) running on the PE/CE interface.)

与路由目标T相关联的任何路由必须分配给每个具有与路由目标T相关联的VRF的PE路由器。当PE路由器接收到此类路由时,它有资格安装在与路由目标T相关联的PE VRF中。(它是否实际安装取决于BGP决策过程的结果,以及在PE/CE接口上运行的IGP(即域内路由协议)决策过程的结果。)

A Route Target attribute can be thought of as identifying a set of sites. (Though it would be more precise to think of it as identifying a set of VRFs.) Associating a particular Route Target attribute with a route allows that route to be placed in the VRFs that are used for routing traffic that is received from the corresponding sites.


There is a set of Route Targets that a PE router attaches to a route received from site S; these may be called the "Export Targets". And there is a set of Route Targets that a PE router uses to determine whether a route received from another PE router could be placed in the VRF associated with site S; these may be called the "Import Targets". The two sets are distinct, and need not be the same. Note that a particular VPN-IPv4 route is only eligible for installation in a particular VRF if there is some Route Target that is both one of the route's Route Targets and one of the VRF's Import Targets.


The function performed by the Route Target attribute is similar to that performed by the BGP Communities attribute. However, the format of the latter is inadequate for present purposes, since it allows only a 2-byte numbering space. It is desirable to structure the format, similar to what we have described for RDs (see Section 4.2), so that a type field defines the length of an administrator field, and the remainder of the attribute is a number from the specified administrator's numbering space. This can be done using BGP Extended Communities. The Route Targets discussed herein are encoded as BGP Extended Community Route Targets [BGP-EXTCOMM]. They are structured similarly to the RDs.


When a BGP speaker has received more than one route to the same VPN-IPv4 prefix, the BGP rules for route preference are used to choose which VPN-IPv4 route is installed by BGP.


Note that a route can only have one RD, but it can have multiple Route Targets. In BGP, scalability is improved if one has a single route with multiple attributes, as opposed to multiple routes. One


could eliminate the Route Target attribute by creating more routes (i.e., using more RDs), but the scaling properties would be less favorable.


How does a PE determine which Route Target attributes to associate with a given route? There are a number of different possible ways. The PE might be configured to associate all routes that lead to a specified site with a specified Route Target. Or the PE might be configured to associate certain routes leading to a specified site with one Route Target, and certain with another.


If the PE and the CE are themselves BGP peers (see Section 7), then the SP may allow the customer, within limits, to specify how its routes are to be distributed. The SP and the customer would need to agree in advance on the set of RTs that are allowed to be attached to the customer's VPN routes. The CE could then attach one or more of those RTs to each IP route that it distributes to the PE. This gives the customer the freedom to specify in real time, within agreed-upon limits, its route distribution policies. If the CE is allowed to attach RTs to its routes, the PE MUST filter out all routes that contain RTs that the customer is not allowed to use. If the CE is not allowed to attach RTs to its routes, but does so anyway, the PE MUST remove the RT before converting the customer's route to a VPN-IPv4 route.


4.3.2. Route Distribution Among PEs by BGP
4.3.2. 基于BGP的PEs间路由分配

If two sites of a VPN attach to PEs that are in the same Autonomous System, the PEs can distribute VPN-IPv4 routes to each other by means of an IBGP connection between them. (The term "IBGP" refers to the set of protocols and procedures used when there is a BGP connection between two BGP speakers in the same Autonomous System. This is distinguished from "EBGP", the set of procedures used between two BGP speakers in different Autonomous Systems.) Alternatively, each can have an IBGP connection to a route reflector [BGP-RR].


When a PE router distributes a VPN-IPv4 route via BGP, it uses its own address as the "BGP next hop". This address is encoded as a VPN-IPv4 address with an RD of 0. ([BGP-MP] requires that the next hop address be in the same address family as the Network Layer Reachability Information (NLRI).) It also assigns and distributes an MPLS label. (Essentially, PE routers distribute not VPN-IPv4 routes, but Labeled VPN-IPv4 routes. Cf. [MPLS-BGP].) When the PE processes a received packet that has this label at the top of the stack, the PE will pop the stack, and process the packet appropriately.


The PE may distribute the exact set of routes that appears in the VRF, or it may perform summarization and distribute aggregates of those routes, or it may do some of one and some of the other.


Suppose that a PE has assigned label L to route R, and has distributed this label mapping via BGP. If R is an aggregate of a set of routes in the VRF, the PE will know that packets from the backbone that arrive with this label must have their destination addresses looked up in a VRF. When the PE looks up the label in its Label Information Base, it learns which VRF must be used. On the other hand, if R is not an aggregate, then when the PE looks up the label, it learns the egress attachment circuit, as well as the encapsulation header for the packet. In this case, no lookup in the VRF is done.


We would expect that the most common case would be the case where the route is NOT an aggregate. The case where it is an aggregate can be very useful though if the VRF contains a large number of host routes (e.g., as in dial-in), or if the VRF has an associated Local Area Network (LAN) interface (where there is a different outgoing layer 2 header for each system on the LAN, but a route is not distributed for each such system).


Whether or not each route has a distinct label is an implementation matter. There are a number of possible algorithms one could use to determine whether two routes get assigned the same label:


- One may choose to have a single label for an entire VRF, so that a single label is shared by all the routes from that VRF. Then when the egress PE receives a packet with that label, it must look up the packet's IP destination address in that VRF (the packet's "egress VRF"), in order to determine the packet's egress attachment circuit and the corresponding data link encapsulation.

- 可以为整个VRF选择一个标签,以便来自该VRF的所有路由共享一个标签。然后,当出口PE接收到具有该标签的分组时,它必须在该VRF(分组的“出口VRF”)中查找分组的IP目的地地址,以便确定分组的出口连接电路和相应的数据链路封装。

- One may choose to have a single label for each attachment circuit, so that a single label is shared by all the routes with the same "outgoing attachment circuit". This enables one to avoid doing a lookup in the egress VRF, though some sort of lookup may need to be done in order to determine the data link encapsulation, e.g., an Address Resolution Protocol (ARP) lookup.

- 可以为每个连接回路选择一个标签,以便具有相同“输出连接回路”的所有路由共享一个标签。这使得人们能够避免在出口VRF中进行查找,尽管可能需要进行某种查找以确定数据链路封装,例如,地址解析协议(ARP)查找。

- One may choose to have a distinct label for each route. Then if a route is potentially reachable over more than one attachment circuit, the PE/CE routing can switch the preferred path for a route from one attachment circuit to another, without there being any need to distribute new a label for that route.

- 可以为每条路线选择不同的标签。然后,如果路由可能可通过多个连接电路到达,则PE/CE路由可以将路由的首选路径从一个连接电路切换到另一个连接电路,而无需为该路由分发新标签。

There may be other possible algorithms as well. The choice of algorithm is entirely at the discretion of the egress PE, and is otherwise transparent.


In using BGP-distributed MPLS labels in this manner, we presuppose that an MPLS packet carrying such a label can be tunneled from the router that installs the corresponding BGP-distributed route to the router that is the BGP next hop of that route. This requires either that a label switched path exist between those two routers or else that some other tunneling technology (e.g., [MPLS-in-IP-GRE]) can be used between them.

在以这种方式使用BGP分布式MPLS标签时,我们假设携带这种标签的MPLS包可以从安装相应BGP分布式路由的路由器隧道到作为该路由的BGP下一跳的路由器。这需要在这两个路由器之间存在标签交换路径,或者可以在它们之间使用其他隧道技术(例如,[MPLS in IP GRE])。

This tunnel may follow a "best effort" route, or it may follow a traffic-engineered route. Between a given pair of routers, there may be one such tunnel, or there may be several, perhaps with different Quality of Service (QoS) characteristics. All that matters for the VPN architecture is that some such tunnel exists. To ensure interoperability among systems that implement this VPN architecture using MPLS label switched paths as the tunneling technology, all such systems MUST support Label Distribution Protocol (LDP) [MPLS-LDP]. In particular, Downstream Unsolicited mode MUST be supported on interfaces that are neither Label Controlled ATM (LC-ATM) [MPLS-ATM] nor Label Controlled Frame Relay (LC-FR) [MPLS-FR] interfaces, and Downstream on Demand mode MUST be supported on LC-ATM interfaces and LC-FR interfaces.


If the tunnel follows a best-effort route, then the PE finds the route to the remote endpoint by looking up its IP address in the default forwarding table.


A PE router, UNLESS it is a route reflector (see Section 4.3.3) or an Autonomous System Border Router (ASBR) for an inter-provider VPN (see Section 10), should not install a VPN-IPv4 route unless it has at least one VRF with an Import Target identical to one of the route's Route Target attributes. Inbound filtering should be used to cause such routes to be discarded. If a new Import Target is later added to one of the PE's VRFs (a "VPN Join" operation), it must then acquire the routes it may previously have discarded. This can be done using the refresh mechanism described in [BGP-RFSH]. The outbound route filtering mechanism of [BGP-ORF] can also be used to advantage to make the filtering more dynamic.


Similarly, if a particular Import Target is no longer present in any of a PE's VRFs (as a result of one or more "VPN Prune" operations), the PE may discard all routes that, as a result, no longer have any of the PE's VRF's Import Targets as one of their Route Target attributes.


A router that is not attached to any VPN and that is not a Route Reflector (i.e., a P router) never installs any VPN-IPv4 routes at all.


Note that VPN Join and Prune operations are non-disruptive and do not require any BGP connections to be brought down, as long as the refresh mechanism of [BGP-RFSH] is used.


As a result of these distribution rules, no one PE ever needs to maintain all routes for all VPNs; this is an important scalability consideration.


4.3.3. Use of Route Reflectors
4.3.3. 路线反射器的使用

Rather than having a complete IBGP mesh among the PEs, it is advantageous to make use of BGP Route Reflectors [BGP-RR] to improve scalability. All the usual techniques for using route reflectors to improve scalability (e.g., route reflector hierarchies) are available.


Route reflectors are the only systems that need to have routing information for VPNs to which they are not directly attached. However, there is no need to have any one route reflector know all the VPN-IPv4 routes for all the VPNs supported by the backbone.


We outline below two different ways to partition the set of VPN-IPv4 routes among a set of route reflectors.


1. Each route reflector is preconfigured with a list of Route Targets. For redundancy, more than one route reflector may be preconfigured with the same list. A route reflector uses the preconfigured list of Route Targets to construct its inbound route filtering. The route reflector may use the techniques of [BGP-ORF] to install on each of its peers (regardless of whether the peer is another route reflector or a PE) the set of Outbound Route Filters (ORFs) that contains the list of its preconfigured Route Targets. Note that route reflectors should accept ORFs from other route reflectors, which means that route reflectors should advertise the ORF capability to other route reflectors.

1. 每个路由反射器都预先配置了路由目标列表。对于冗余,可以使用同一列表预先配置多个路由反射器。路由反射器使用预先配置的路由目标列表来构建其入站路由过滤。路由反射器可使用[BGP-ORF]的技术在其每个对等体(无论该对等体是另一路由反射器还是PE)上安装包含其预配置路由目标列表的出站路由过滤器(ORF)集合。注意,路线反射器应接受来自其他路线反射器的ORF,这意味着路线反射器应向其他路线反射器公布ORF能力。

A service provider may modify the list of preconfigured Route Targets on a route reflector. When this is done, the route reflector modifies the ORFs it installs on all of its IBGP peers. To reduce the frequency of configuration changes on route reflectors, each route reflector may be preconfigured with a block of Route Targets. This way, when a new Route Target is needed for a new VPN, there is already one or more


route reflectors that are (pre)configured with this Route Target.


Unless a given PE is a client of all route reflectors, when a new VPN is added to the PE ("VPN Join"), it will need to become a client of the route reflector(s) that maintain routes for that VPN. Likewise, deleting an existing VPN from the PE ("VPN Prune") may result in a situation where the PE no longer needs to be a client of some route reflector(s). In either case, the Join or Prune operation is non-disruptive (as long as [BGP-RFSH] is used, and never requires a BGP connection to be brought down, only to be brought right back up.


(By "adding a new VPN to a PE", we really mean adding a new import Route Target to one of its VRFs, or adding a new VRF with an import Route Target not had by any of the PE's other VRFs.)


2. Another method is to have each PE be a client of some subset of the route reflectors. A route reflector is not preconfigured with the list of Route Targets, and does not perform inbound route filtering of routes received from its clients (PEs); rather, it accepts all the routes received from all of its clients (PEs). The route reflector keeps track of the set of the Route Targets carried by all the routes it receives. When the route reflector receives from its client a route with a Route Target that is not in this set, this Route Target is immediately added to the set. On the other hand, when the route reflector no longer has any routes with a particular Route Target that is in the set, the route reflector should delay (by a few hours) the deletion of this Route Target from the set.

2. 另一种方法是让每个PE成为路由反射器的某个子集的客户端。路由反射器未预先配置路由目标列表,并且不对从其客户端(PE)接收的路由执行入站路由过滤;相反,它接受从所有客户端(PE)接收的所有路由。路由反射器跟踪其接收的所有路由所承载的路由目标集。当路由反射器从其客户端接收到一条路由,且该路由目标不在此集合中时,该路由目标将立即添加到集合中。另一方面,当路由反射器不再具有具有集合中的特定路由目标的任何路由时,路由反射器应当延迟(几小时)从集合中删除该路由目标。

The route reflector uses this set to form the inbound route filters that it applies to routes received from other route reflectors. The route reflector may also use ORFs to install the appropriate outbound route filtering on other route reflectors. Just like with the first approach, a route reflector should accept ORFs from other route reflectors. To accomplish this, a route reflector advertises ORF capability to other route reflectors.

route reflector使用此集合来形成入站路由筛选器,该筛选器应用于从其他路由reflector接收的路由。路由反射器还可以使用ORF在其他路由反射器上安装适当的出站路由过滤。与第一种方法一样,路由反射器应该接受来自其他路由反射器的ORF。为此,路由反射器向其他路由反射器宣传ORF能力。

When the route reflector changes the set, it should immediately change its inbound route filtering. In addition, if the route reflector uses ORFs, then the ORFs have to be immediately changed to reflect the changes in the set. If the route reflector doesn't use ORFs, and a new Route Target is added to


the set, the route reflector, after changing its inbound route filtering, must issue BGP Refresh to other route reflectors.


The delay of "a few hours" mentioned above allows a route reflector to hold onto routes with a given RT, even after it loses the last of its clients that are interested in such routes. This protects against the need to reacquire all such routes if the clients' "disappearance" is only temporary.


With this procedure, VPN Join and Prune operations are also non-disruptive.


Note that this technique will not work properly if some client PE has a VRF with an import Route Target that is not one of its export Route Targets.


In these procedures, a PE router which attaches to a particular VPN "auto-discovers" the other PEs that attach to the same VPN. When a new PE router is added, or when an existing PE router attaches to a new VPN, no reconfiguration of other PE routers is needed.


Just as there is no one PE router that needs to know all the VPN-IPv4 routes supported over the backbone, these distribution rules ensure that there is no one Route Reflector (RR) that needs to know all the VPN-IPv4 routes supported over the backbone. As a result, the total number of such routes that can be supported over the backbone is not bounded by the capacity of any single device, and therefore can increase virtually without bound.


4.3.4. How VPN-IPv4 NLRI Is Carried in BGP
4.3.4. BGP中如何承载VPN-IPv4 NLRI

The BGP Multiprotocol Extensions [BGP-MP] are used to encode the NLRI. If the Address Family Identifier (AFI) field is set to 1, and the Subsequent Address Family Identifier (SAFI) field is set to 128, the NLRI is an MPLS-labeled VPN-IPv4 address. AFI 1 is used since the network layer protocol associated with the NLRI is still IP. Note that this VPN architecture does not require the capability to distribute unlabeled VPN-IPv4 addresses.

BGP多协议扩展[BGP-MP]用于对NLRI进行编码。如果地址族标识符(AFI)字段设置为1,后续地址族标识符(SAFI)字段设置为128,则NLRI是标记为VPN-IPv4地址的MPLS。由于与NLRI关联的网络层协议仍然是IP,因此使用AFI 1。请注意,此VPN体系结构不需要分发未标记的VPN-IPv4地址的功能。

In order for two BGP speakers to exchange labeled VPN-IPv4 NLRI, they must use BGP Capabilities Advertisement to ensure that they both are capable of properly processing such NLRI. This is done as specified in [BGP-MP], by using capability code 1 (multiprotocol BGP), with an AFI of 1 and an SAFI of 128.

为了让两个BGP扬声器交换带标签的VPN-IPv4 NLRI,他们必须使用BGP功能播发,以确保他们都能够正确处理此类NLRI。这是按照[BGP-MP]中的规定完成的,使用能力代码1(多协议BGP),AFI为1,SAFI为128。

The labeled VPN-IPv4 NLRI itself is encoded as specified in [MPLS-BGP], where the prefix consists of an 8-byte RD followed by an IPv4 prefix.

标记的VPN-IPv4 NLRI本身按照[MPLS-BGP]中的规定进行编码,其中前缀由8字节RD和IPv4前缀组成。

4.3.5. Building VPNs Using Route Targets
4.3.5. 使用路由目标构建VPN

By setting up the Import Targets and Export Targets properly, one can construct different kinds of VPNs.


Suppose it is desired to create a fully meshed closed user group, i.e., a set of sites where each can send traffic directly to the other, but traffic cannot be sent to or received from other sites. Then each site is associated with a VRF, a single Route Target attribute is chosen, that Route Target is assigned to each VRF as both the Import Target and the Export Target, and that Route Target is not assigned to any other VRFs as either the Import Target or the Export Target.


Alternatively, suppose one desired, for whatever reason, to create a "hub and spoke" kind of VPN. This could be done by the use of two Route Target values, one meaning "Hub" and one meaning "Spoke". At the VRFs attached to the hub sites, "Hub" is the Export Target and


"Spoke" is the Import Target. At the VRFs attached to the spoke site, "Hub" is the Import Target and "Spoke" is the Export Target.


Thus, the methods for controlling the distribution of routing information among various sets of sites are very flexible, which in turn provides great flexibility in constructing VPNs.


4.3.6. Route Distribution Among VRFs in a Single PE
4.3.6. 单个PE中VRF之间的路由分布

It is possible to distribute routes from one VRF to another, even if both VRFs are in the same PE, even though in this case one cannot say that the route has been distributed by BGP. Nevertheless, the decision to distribute a particular route from one VRF to another within a single PE is the same decision that would be made if the VRFs were on different PEs. That is, it depends on the Route Target attribute that is assigned to the route (or would be assigned if the route were distributed by BGP), and the import target of the second VRF.


5. Forwarding
5. 转发

If the intermediate routers in the backbone do not have any information about the routes to the VPNs, how are packets forwarded from one VPN site to another?


When a PE receives an IP packet from a CE device, it chooses a particular VRF in which to look up the packet's destination address. This choice is based on the packet's ingress attachment circuit.


Assume that a match is found. As a result we learn the packet's "next hop".


If the packet's next hop is reached directly over a VRF attachment circuit from this PE (i.e., the packet's egress attachment circuit is on the same PE as its ingress attachment circuit), then the packet is sent on the egress attachment circuit, and no MPLS labels are pushed onto the packet's label stack.


If the ingress and egress attachment circuits are on the same PE, but are associated with different VRFs, and if the route that best matches the destination address in the ingress attachment circuit's VRF is an aggregate of several routes in the egress attachment circuit's VRF, it may be necessary to look up the packet's destination address in the egress VRF as well.


If the packet's next hop is NOT reached through a VRF attachment circuit, then the packet must travel at least one hop through the backbone. The packet thus has a "BGP Next Hop", and the BGP Next Hop will have assigned an MPLS label for the route that best matches the packet's destination address. Call this label the "VPN route label". The IP packet is turned into an MPLS packet with the VPN route label as the sole label on the label stack.


The packet must then be tunneled to the BGP Next Hop.


If the backbone supports MPLS, this is done as follows:


- The PE routers (and any Autonomous System border routers) that redistribute VPN-IPv4 addresses need to insert /32 address prefixes for themselves into the IGP routing tables of the backbone. This enables MPLS, at each node in the backbone network, to assign a label corresponding to the route to each PE router. To ensure interoperability among different implementations, it is required to support LDP for setting up the label switched paths across the backbone. However, other methods of setting up these label switched paths are also possible. (Some of these other methods may not require the presence of the /32 address prefixes in the IGP.)

- 重新分配VPN-IPv4地址的PE路由器(以及任何自治系统边界路由器)需要将/32地址前缀插入主干网的IGP路由表中。这使得主干网中每个节点上的MPLS能够将与路由对应的标签分配给每个PE路由器。为了确保不同实现之间的互操作性,需要支持LDP来设置主干上的标签交换路径。然而,设置这些标签交换路径的其他方法也是可能的。(其中一些其他方法可能不要求IGP中存在/32地址前缀。)

- If there are any traffic engineering tunnels to the BGP next hop, and if one or more of those is available for use by the packet in question, one of these tunnels is chosen. This tunnel will be associated with an MPLS label, the "tunnel label". The tunnel label gets pushed on the MPLS label stack, and the packet is forwarded to the tunnel's next hop.

- 如果存在到BGP下一跳的任何流量工程隧道,并且如果其中一个或多个隧道可供所讨论的分组使用,则选择这些隧道中的一个。此隧道将与MPLS标签“隧道标签”相关联。隧道标签被推送到MPLS标签堆栈上,数据包被转发到隧道的下一跳。

- Otherwise,

- 否则

* The packet will have an "IGP Next Hop", which is the next hop along the IGP route to the BGP Next Hop.

* 数据包将有一个“IGP下一跳”,这是沿IGP路由到BGP下一跳的下一跳。

* If the BGP Next Hop and the IGP Next Hop are the same, and if penultimate hop popping is used, the packet is then sent to the IGP Next Hop, carrying only the VPN route label.

* 如果BGP下一个跃点和IGP下一个跃点相同,并且如果使用倒数第二个跃点弹出,则数据包随后被发送到IGP下一个跃点,仅携带VPN路由标签。

* Otherwise, the IGP Next Hop will have assigned a label for the route that best matches the address of the BGP Next Hop. Call this the "tunnel label". The tunnel label gets pushed on as the packet's top label. The packet is then forwarded to the IGP Next Hop.

* 否则,IGP下一跳将为路由分配一个与BGP下一跳地址最匹配的标签。称之为“隧道标签”。隧道标签作为数据包的顶部标签被推上。然后,该分组被转发到下一跳的IGP。

- MPLS will then carry the packet across the backbone to the BGP Next Hop, where the VPN label will be examined.

- 然后,MPLS将通过主干将数据包传送到BGP下一跳,在那里将检查VPN标签。

If the backbone does not support MPLS, the MPLS packet carrying only the VPN route label may be tunneled to the BGP Next Hop using the techniques of [MPLS-in-IP-GRE]. When the packet emerges from the tunnel, it will be at the BGP Next Hop, where the VPN route label will be examined.

如果主干网不支持MPLS,则可以使用[MPLS in IP GRE]的技术将仅携带VPN路由标签的MPLS分组通过隧道传送到BGP下一跳。当数据包从隧道中出现时,它将位于BGP下一跳,在那里将检查VPN路由标签。

At the BGP Next Hop, the treatment of the packet depends on the VPN route label (see Section 4.3.2). In many cases, the PE will be able to determine, from this label, the attachment circuit over which the packet should be transmitted (to a CE device), as well as the proper data link layer header for that interface. In other cases, the PE may only be able to determine that the packet's destination address needs to be looked up in a particular VRF before being forwarded to a CE device. There are also intermediate cases in which the VPN route label may determine the packet's egress attachment circuit, but a lookup (e.g., ARP) still needs to be done in order to determine the packet's data link header on that attachment circuit.


Information in the MPLS header itself, and/or information associated with the label, may also be used to provide QoS on the interface to the CE.


In any event, if the packet was an unlabeled IP packet when it arrived at its ingress PE, it will again be an unlabeled packet when it leaves its egress PE.


The fact that packets with VPN route labels are tunneled through the backbone is what makes it possible to keep all the VPN routes out of the P routers. This is crucial to ensuring the scalability of the


scheme. The backbone does not even need to have routes to the CEs, only to the PEs.


With respect to the tunnels, it is worth noting that this specification:


- DOES NOT require that the tunnels be point-to-point; multipoint-to-point can be used;

- 不要求隧道是点对点的;可以使用多点对点;

- DOES NOT require that there be any explicit setup of the tunnels, either via signaling or via manual configuration;

- 不要求通过信号或手动配置明确设置隧道;

- DOES NOT require that there be any tunnel-specific signaling;

- 不要求有任何特定于隧道的信号;

- DOES NOT require that there be any tunnel-specific state in the P or PE routers, beyond what is necessary to maintain the routing information and (if used) the MPLS label information.

- 除了维护路由信息和(如果使用)MPLS标签信息所必需的状态外,不要求P或PE路由器中存在任何特定于隧道的状态。

Of course, this specification is compatible with the use of point-to-point tunnels that must be explicitly configured and/or signaled, and in some situations there may be reasons for using such tunnels.


The considerations that are relevant to choosing a particular tunneling technology are outside the scope of this specification.


6. Maintaining Proper Isolation of VPNs
6. 保持vpn的适当隔离

To maintain proper isolation of one VPN from another, it is important that no router in the backbone accept a tunneled packet from outside the backbone, unless it is sure that both endpoints of that tunnel are outside the backbone.


If MPLS is being used as the tunneling technology, this means that a router in the backbone MUST NOT accept a labeled packet from any adjacent non-backbone device unless the following two conditions hold:


1. the label at the top of the label stack was actually distributed by that backbone router to that non-backbone device, and

1. 标签栈顶部的标签实际上是由主干路由器分发给非主干设备的,并且

2. the backbone router can determine that use of that label will cause the packet to leave the backbone before any labels lower in the stack will be inspected, and before the IP header will be inspected.

2. 主干路由器可以确定,在检查堆栈中较低的任何标签之前,以及在检查IP报头之前,使用该标签将导致数据包离开主干。

The first condition ensure that any labeled packets received from non-backbone routers have a legitimate and properly assigned label at


the top of the label stack. The second condition ensures that the backbone routers will never look below that top label. Of course, the simplest way to meet these two conditions is just to have the backbone devices refuse to accept labeled packets from non-backbone devices.


If MPLS is not being used as the tunneling technology, then filtering must be done to ensure that an MPLS-in-IP or MPLS-in-GRE packet can be accepted into the backbone only if the packet's IP destination address will cause it to be sent outside the backbone.


7. How PEs Learn Routes from CEs
7. PEs如何从CEs学习路线

The PE routers that attach to a particular VPN need to know, for each attachment circuit leading to that VPN, which of the VPN's addresses should be reached over that attachment circuit.


The PE translates these addresses into VPN-IPv4 addresses, using a configured RD. The PE then treats these VPN-IPv4 routes as input to BGP. Routes from a VPN site are NOT leaked into the backbone's IGP.


Exactly which PE/CE route distribution techniques are possible depends on whether or not a particular CE is in a "transit VPN". A "transit VPN" is one that contains a router that receives routes from a "third party" (i.e., from a router that is not in the VPN, but is not a PE router) and that redistributes those routes to a PE router. A VPN that is not a transit VPN is a "stub VPN". The vast majority of VPNs, including just about all corporate enterprise networks, would be expected to be "stubs" in this sense.


The possible PE/CE distribution techniques are:


1. Static routing (i.e., configuration) may be used. (This is likely to be useful only in stub VPNs.)

1. 可以使用静态路由(即配置)。(这可能仅在存根VPN中有用。)

2. PE and CE routers may be Routing Information Protocol (RIP) [RIP] peers, and the CE may use RIP to tell the PE router the set of address prefixes that are reachable at the CE router's site. When RIP is configured in the CE, care must be taken to ensure that address prefixes from other sites (i.e., address prefixes learned by the CE router from the PE router) are never advertised to the PE. More precisely: if a PE router, say, PE1, receives a VPN-IPv4 route R1, and as a result distributes an IPv4 route R2 to a CE, then R2 must not be distributed back from that CE's site to a PE router, say, PE2, (where PE1 and PE2 may be the same router or different routers), unless PE2 maps R2 to a VPN-IPv4 route that is different than (i.e., contains a different RD than) R1.

2. PE和CE路由器可以是路由信息协议(RIP)[RIP]对等方,并且CE可以使用RIP来告诉PE路由器可在CE路由器的站点上访问的地址前缀集。当在CE中配置RIP时,必须注意确保从不向PE播发来自其他站点的地址前缀(即CE路由器从PE路由器学习的地址前缀)。更准确地说:如果PE路由器(例如PE1)接收到VPN-IPv4路由R1,并因此将IPv4路由R2分发给CE,则R2不得从该CE的站点分发回PE路由器(例如PE2)(其中PE1和PE2可能是相同的路由器或不同的路由器),除非PE2将R2映射到与之不同的VPN-IPv4路由(即,包含与)R1不同的RD。

3. The PE and CE routers may be OSPF peers. A PE router that is an OSPF peer of a CE router appears, to the CE router, to be an area 0 router. If a PE router is an OSPF peer of CE routers that are in distinct VPNs, the PE must of course be running multiple instances of OSPF.

3. PE和CE路由器可以是OSPF对等方。作为CE路由器的OSPF对等方的PE路由器在CE路由器看来是区域0路由器。如果PE路由器是位于不同VPN中的CE路由器的OSPF对等方,则PE当然必须运行多个OSPF实例。

IPv4 routes that the PE learns from the CE via OSPF are redistributed into BGP as VPN-IPv4 routes. Extended Community attributes are used to carry, along with the route, all the information needed to enable the route to be distributed to other CE routers in the VPN in the proper type of OSPF Link State Advertisement (LSA). OSPF route tagging is used to ensure that routes received from the MPLS/BGP backbone are not sent back into the backbone.


Specification of the complete set of procedures for the use of OSPF between PE and CE can be found in [VPN-OSPF] and [OSPF-2547-DNBIT].


4. The PE and CE routers may be BGP peers, and the CE router may use BGP (in particular, EBGP to tell the PE router the set of address prefixes that are at the CE router's site. (This technique can be used in stub VPNs or transit VPNs.)

4. PE和CE路由器可以是BGP对等方,CE路由器可以使用BGP(特别是EBGP来告诉PE路由器位于CE路由器站点的地址前缀集。(此技术可用于存根VPN或传输VPN。)

This technique has a number of advantages over the others:


a) Unlike the IGP alternatives, this does not require the PE to run multiple routing algorithm instances in order to talk to multiple CEs.

a) 与IGP备选方案不同,这不需要PE运行多个路由算法实例来与多个CE对话。

b) BGP is explicitly designed for just this function: passing routing information between systems run by different administrations.

b) BGP的明确设计就是为了实现这一功能:在由不同管理机构运行的系统之间传递路由信息。

c) If the site contains "BGP backdoors", i.e., routers with BGP connections to routers other than PE routers, this procedure will work correctly in all circumstances. The other procedures may or may not work, depending on the precise circumstances.

c) 如果站点包含“BGP后门”,即与PE路由器以外的路由器具有BGP连接的路由器,则此过程将在所有情况下正常工作。根据具体情况,其他程序可能有效,也可能无效。

d) Use of BGP makes it easy for the CE to pass attributes of the routes to the PE. A complete specification of the set of attributes and their use is outside the scope of this document. However, some examples of the way this may be used are the following:

d) BGP的使用使得CE可以轻松地将路由属性传递给PE。属性集及其使用的完整规范不在本文档范围内。但是,以下是一些可能使用该方法的示例:

- The CE may suggest a particular Route Target for each route, from among the Route Targets that the PE is authorized to attach to the route. The PE would then attach only the suggested Route Target, rather than the full set. This gives the CE administrator some dynamic control of the distribution of routes from the CE.

- CE可以从PE被授权连接到路由的路由目标中,为每条路由建议一个特定的路由目标。然后,PE将只附加建议的路由目标,而不是全套。这使CE管理员能够动态控制来自CE的路由分布。

- Additional types of Extended Community attributes may be defined, where the intention is to have those attributes passed transparently (i.e., without being changed by the PE routers) from CE to CE. This would allow CE administrators to implement additional route filtering, beyond that which is done by the PEs. This additional filtering would not require coordination with the SP.

- 可以定义其他类型的扩展社区属性,其中意图是使这些属性从CE透明地传递到CE(即,不被PE路由器改变)。这将允许CE管理员实施额外的路由过滤,而不仅仅是由PEs完成的过滤。此附加筛选不需要与SP协调。

On the other hand, using BGP may be something new for the CE administrators.


If a site is not in a transit VPN, note that it need not have a unique Autonomous System Number (ASN). Every CE whose site is not in a transit VPN can use the same ASN. This can be chosen from the private ASN space, and it will be stripped out by the PE. Routing loops are prevented by use of the Site of Origin attribute (see below).

如果站点不在transit VPN中,请注意,它不需要具有唯一的自治系统号(ASN)。站点不在transit VPN中的每个CE都可以使用相同的ASN。这可以从专用ASN空间中选择,并由PE剥离。使用“源站点”属性可以防止路由循环(请参见下文)。

What if a set of sites constitutes a transit VPN? This will generally be the case only if the VPN is itself an Internet Service Provider's (ISP's) network, where the ISP is itself buying backbone services from another SP. The latter SP may be called a "carrier's carrier". In this case, the best way to provide the VPN is to have the CE routers support MPLS, and to use the technique described in Section 9.


When we do not need to distinguish among the different ways in which a PE can be informed of the address prefixes that exist at a given site, we will simply say that the PE has "learned" the routes from that site. This includes the case where the PE has been manually configured with the routes.


Before a PE can redistribute a VPN-IPv4 route learned from a site, it must assign a Route Target attribute (see Section 4.3.1) to the route, and it may assign a Site of Origin attribute to the route.


The Site of Origin attribute, if used, is encoded as a Route Origin Extended Community [BGP-EXTCOMM]. The purpose of this attribute is to uniquely identify the set of routes learned from a particular


site. This attribute is needed in some cases to ensure that a route learned from a particular site via a particular PE/CE connection is not distributed back to the site through a different PE/CE connection. It is particularly useful if BGP is being used as the PE/CE protocol, but different sites have not been assigned distinct ASNs.


8. How CEs Learn Routes from PEs
8. CEs如何从PEs学习路线

In this section, we assume that the CE device is a router.


If the PE places a particular route in the VRF it uses to route packets received from a particular CE, then in general, the PE may distribute that route to the CE. Of course, the PE may distribute that route to the CE only if this is permitted by the rules of the PE/CE protocol. (For example, if a particular PE/CE protocol has "split horizon", certain routes in the VRF cannot be redistributed back to the CE.) We add one more restriction on the distribution of routes from PE to CE: if a route's Site of Origin attribute identifies a particular site, that route must never be redistributed to any CE at that site.


In most cases, however, it will be sufficient for the PE to simply distribute the default route to the CE. (In some cases, it may even be sufficient for the CE to be configured with a default route pointing to the PE.) This will generally work at any site that does not itself need to distribute the default route to other sites. (E.g., if one site in a corporate VPN has the corporation's access to the Internet, that site might need to have default distributed to the other site, but one could not distribute default to that site itself.)


Whatever procedure is used to distribute routes from CE to PE will also be used to distribute routes from PE to CE.


9. Carriers' Carriers
9. 承运人的承运人

Sometimes a VPN may actually be the network of an ISP, with its own peering and routing policies. Sometimes a VPN may be the network of an SP that is offering VPN services in turn to its own customers. VPNs like these can also obtain backbone service from another SP, the "carrier's carrier", using essentially the same methods described in this document. However, it is necessary in these cases that the CE routers support MPLS. In particular:


- The CE routers should distribute to the PE routers ONLY those routes that are internal to the VPN. This allows the VPN to be handled as a stub VPN.

- CE路由器应仅将VPN内部的路由分配给PE路由器。这允许VPN作为存根VPN处理。

- The CE routers should support MPLS, in that they should be able to receive labels from the PE routers, and send labeled packets to the PE routers. They do not need to distribute labels of their own, though.

- CE路由器应该支持MPLS,因为它们应该能够从PE路由器接收标签,并向PE路由器发送标签数据包。不过,他们不需要分发自己的标签。

- The PE routers should distribute, to the CE routers, labels for the routes they distribute to the CE routers.

- PE路由器应向CE路由器分发其分发给CE路由器的路由标签。

The PE must not distribute the same label to two different CEs unless one of the following conditions holds:


* The two CEs are associated with exactly the same set of VRFs;

* 两个CE与完全相同的VRF集合相关联;

* The PE maintains a different Incoming Label Map ([MPLS-ARCH]) for each CE.

* PE为每个CE维护不同的传入标签映射([MPLS-ARCH])。

Further, when the PE receives a labeled packet from a CE, it must verify that the top label is one that was distributed to that CE.


- Routers at the different sites should establish BGP connections among themselves for the purpose of exchanging external routes (i.e., routes that lead outside of the VPN).

- 不同站点的路由器应在它们之间建立BGP连接,以交换外部路由(即通向VPN外部的路由)。

- All the external routes must be known to the CE routers.

- CE路由器必须知道所有外部路由。

Then when a CE router looks up a packet's destination address, the routing lookup will resolve to an internal address, usually the address of the packet's BGP next hop. The CE labels the packet appropriately and sends the packet to the PE. The PE, rather than looking up the packet's IP destination address in a VRF, uses the packet's top MPLS label to select the BGP next hop. As a result, if the BGP next hop is more than one hop away, the top label will be replaced by two labels, a tunnel label and a VPN route label. If the BGP next hop is one hop away, the top label may be replaced by just the VPN route label. If the ingress PE is also the egress PE, the top label will just be popped. When the packet is sent from its egress PE to a CE, the packet will have one fewer MPLS labels than it had when it was first received by its ingress PE.


In the above procedure, the CE routers are the only routers in the VPN that need to support MPLS. If, on the other hand, all the routers at a particular VPN site support MPLS, then it is no longer required that the CE routers know all the external routes. All that is required is that the external routes be known to whatever routers are responsible for putting the label stack on a hitherto unlabeled packet and that there be label switched path that leads from those routers to their BGP peers at other sites. In this case, for each


internal route that a CE router distributes to a PE router, it must also distribute a label.


10. Multi-AS Backbones
10. 作为主干的多个

What if two sites of a VPN are connected to different Autonomous Systems (e.g., because the sites are connected to different SPs)? The PE routers attached to that VPN will then not be able to maintain IBGP connections with each other, or with a common route reflector. Rather, there needs to be some way to use EBGP to distribute VPN-IPv4 addresses.


There are a number of different ways of handling this case, which we present in order of increasing scalability.


a) VRF-to-VRF connections at the AS (Autonomous System) border routers.

a) AS(自治系统)边界路由器上的VRF到VRF连接。

In this procedure, a PE router in one AS attaches directly to a PE router in another. The two PE routers will be attached by multiple sub-interfaces, at least one for each of the VPNs whose routes need to be passed from AS to AS. Each PE will treat the other as if it were a CE router. That is, the PEs associate each such sub-interface with a VRF, and use EBGP to distribute unlabeled IPv4 addresses to each other.


This is a procedure that "just works", and that does not require MPLS at the border between ASes. However, it does not scale as well as the other procedures discussed below.


b) EBGP redistribution of labeled VPN-IPv4 routes from AS to neighboring AS.

b) EBGP重新分配从AS到相邻AS的标记VPN-IPv4路由。

In this procedure, the PE routers use IBGP to redistribute labeled VPN-IPv4 routes either to an Autonomous System Border Router (ASBR), or to a route reflector of which an ASBR is a client. The ASBR then uses EBGP to redistribute those labeled VPN-IPv4 routes to an ASBR in another AS, which in turn distributes them to the PE routers in that AS, or perhaps to another ASBR which in turn distributes them, and so on.


When using this procedure, VPN-IPv4 routes should only be accepted on EBGP connections at private peering points, as part of a trusted arrangement between SPs. VPN-IPv4 routes should neither be distributed to nor accepted from the public Internet, or from any BGP peers that are not trusted. An ASBR should never accept a labeled packet from an EBGP peer unless it has actually distributed the top label to that peer.


If there are many VPNs having sites attached to different Autonomous Systems, there does not need to be a single ASBR between those two ASes that holds all the routes for all the VPNs; there can be multiple ASBRs, each of which holds only the routes for a particular subset of the VPNs.


This procedure requires that there be a label switched path leading from a packet's ingress PE to its egress PE. Hence the appropriate trust relationships must exist between and among the set of ASes along the path. Also, there must be agreement among the set of SPs as to which border routers need to receive routes with which Route Targets.


c) Multi-hop EBGP redistribution of labeled VPN-IPv4 routes between source and destination ASes, with EBGP redistribution of labeled IPv4 routes from AS to neighboring AS.

c) 源和目标ASE之间标记的VPN-IPv4路由的多跳EBGP重新分配,以及从AS到相邻AS的标记的IPv4路由的EBGP重新分配。

In this procedure, VPN-IPv4 routes are neither maintained nor distributed by the ASBRs. An ASBR must maintain labeled IPv4 /32 routes to the PE routers within its AS. It uses EBGP to distribute these routes to other ASes. ASBRs in any transit ASes will also have to use EBGP to pass along the labeled /32 routes. This results in the creation of a label switched path from the ingress PE router to the egress PE router. Now PE routers in different ASes can establish multi-hop EBGP connections to each other, and can exchange VPN-IPv4 routes over those connections.


If the /32 routes for the PE routers are made known to the P routers of each AS, everything works normally. If the /32 routes for the PE routers are NOT made known to the P routers (other than the ASBRs), then this procedure requires a packet's ingress PE to put a three-label stack on it. The bottom label is assigned by the egress PE, corresponding to the packet's destination address in a particular VRF. The middle label is assigned by the ASBR, corresponding to the /32 route to the egress PE. The top label is assigned by the ingress PE's IGP Next Hop, corresponding to the /32 route to the ASBR.


To improve scalability, one can have the multi-hop EBGP connections exist only between a route reflector in one AS and a route reflector in another. (However, when the route reflectors distribute routes over this connection, they do not modify the BGP next hop attribute of the routes.) The actual PE routers would then only have IBGP connections to the route reflectors in their own AS.

为了提高可伸缩性,可以使多跳EBGP连接仅存在于一个AS中的路由反射器和另一个AS中的路由反射器之间。(但是,当路由反射器通过此连接分发路由时,它们不会修改路由的BGP next hop属性。)实际的PE路由器将只在其自身的AS中具有到路由反射器的IBGP连接。

This procedure is very similar to the "carrier's carrier" procedures described in Section 9. Like the previous procedure, it requires that there be a label switched path leading from a packet's ingress PE to its egress PE.


11. Accessing the Internet from a VPN
11. 从VPN访问Internet

Many VPN sites will need to be able to access the public Internet, as well as to access other VPN sites. The following describes some of the alternative ways of doing this.


1. In some VPNs, one or more of the sites will obtain Internet access by means of an "Internet gateway" (perhaps a firewall) attached to a non-VRF interface to an ISP. The ISP may or may not be the same organization as the SP that is providing the VPN service. Traffic to/from the Internet gateway would then be routed according to the PE router's default forwarding table.

1. 在某些VPN中,一个或多个站点将通过连接到ISP的非VRF接口的“Internet网关”(可能是防火墙)获得Internet访问。ISP可能是也可能不是提供VPN服务的SP所在的组织。然后,将根据PE路由器的默认转发表路由进出Internet网关的流量。

In this case, the sites that have Internet access may be distributing a default route to their PEs, which in turn redistribute it to other PEs and hence into other sites of the VPN. This provides Internet access for all of the VPN's sites.


In order to properly handle traffic from the Internet, the ISP must distribute, to the Internet, routes leading to addresses that are within the VPN. This is completely independent of any of the route distribution procedures described in this document. The internal structure of the VPN will in general not be visible from the Internet; such routes would simply lead to the non-VRF interface that attaches to the VPN's Internet gateway.


In this model, there is no exchange of routes between a PE router's default forwarding table and any of its VRFs. VPN route distribution procedures and Internet route distribution procedures are completely independent.


Note that although some sites of the VPN use a VRF interface to communicate with the Internet, ultimately all packets to/from the Internet traverse a non-VRF interface before leaving/entering the VPN, so we refer to this as "non-VRF Internet access".

请注意,尽管VPN的某些站点使用VRF接口与Internet进行通信,但在离开/进入VPN之前,所有进出Internet的数据包最终都会通过非VRF接口,因此我们将其称为“非VRF Internet访问”。

Note that the PE router to which the non-VRF interface attaches does not necessarily need to maintain all the Internet routes in its default forwarding table. The default forwarding table could have as few as one route, "default", which leads to


another router (probably an adjacent one) that has the Internet routes. A variation of this scheme is to tunnel packets received over the non-VRF interface from the PE router to another router, where this other router maintains the full set of Internet routes.


2. Some VPNs may obtain Internet access via a VRF interface ("VRF Internet access"). If a packet is received by a PE over a VRF interface, and if the packet's destination address does not match any route in the VRF, then it may be matched against the PE's default forwarding table. If a match is made there, the packet can be forwarded natively through the backbone to the Internet, instead of being forwarded by MPLS.

2. 一些VPN可通过VRF接口(“VRF互联网接入”)获得互联网接入。如果PE通过VRF接口接收到数据包,并且数据包的目的地地址与VRF中的任何路由都不匹配,则可以将其与PE的默认转发表相匹配。如果在那里进行了匹配,则数据包可以通过主干本地转发到Internet,而不是通过MPLS转发。

In order for traffic to flow natively in the opposite direction (from Internet to VRF interface), some of the routes from the VRF must be exported to the Internet forwarding table. Needless to say, any such routes must correspond to globally unique addresses.


In this scheme, the default forwarding table might have the full set of Internet routes, or it might have as little as a single default route leading to another router that does have the full set of Internet routes in its default forwarding table.


3. Suppose the PE has the capability to store "non-VPN routes" in a VRF. If a packet's destination address matches a "non-VPN route", then the packet is transmitted natively, rather than being transmitted via MPLS. If the VRF contains a non-VPN default route, all packets for the public Internet will match it, and be forwarded natively to the default route's next hop. At that next hop, the packets' destination addresses will be looked up in the default forwarding table, and may match more specific routes.

3. 假设PE能够在VRF中存储“非VPN路由”。如果数据包的目的地地址与“非VPN路由”匹配,则数据包以本机方式传输,而不是通过MPLS传输。如果VRF包含非VPN默认路由,则公共互联网的所有数据包都将与之匹配,并以本机方式转发到默认路由的下一跳。在下一跳,包的目的地地址将在默认转发表中查找,并且可能匹配更具体的路由。

This technique would only be available if none of the CE routers is distributing a default route.


4. It is also possible to obtain Internet access via a VRF interface by having the VRF contain the Internet routes. Compared with model 2, this eliminates the second lookup, but it has the disadvantage of requiring the Internet routes to be replicated in each such VRF.

4. 通过VRF包含互联网路由,也可以通过VRF接口访问互联网。与模型2相比,这消除了第二次查找,但其缺点是需要在每个这样的VRF中复制Internet路由。

If this technique is used, the SP may want to make its interface to the Internet be a VRF interface, and to use the


techniques of Section 4 to distribute Internet routes, as VPN-IPv4 routes, to other VRFs.


It should be clearly understood that by default, there is no exchange of routes between a VRF and the default forwarding table. This is done ONLY upon agreement between a customer and an SP, and only if it suits the customer's policies.


12. Management VPNs
12. 管理VPN

This specification does not require that the sub-interface connecting a PE router and a CE router be a "numbered" interface. If it is a numbered interface, this specification allows the addresses assigned to the interface to come from either the address space of the VPN or the address space of the SP.


If a CE router is being managed by the Service Provider, then the Service Provider will likely have a network management system that needs to be able to communicate with the CE router. In this case, the addresses assigned to the sub-interface connecting the CE and PE routers should come from the SP's address space, and should be unique within that space. The network management system should itself connect to a PE router (more precisely, be at a site that connects to a PE router) via a VRF interface. The address of the network management system will be exported to all VRFs that are associated with interfaces to CE routers that are managed by the SP. The addresses of the CE routers will be exported to the VRF associated with the network management system, but not to any other VRFs.


This allows communication between the CE and network management system, but does not allow any undesired communication to or among the CE routers.


One way to ensure that the proper route import/exports are done is to use two Route Targets; call them T1 and T2. If a particular VRF interface attaches to a CE router that is managed by the SP, then that VRF is configured to:


- import routes that have T1 attached to them, and

- 导入已附加T1的路由,以及

- attach T2 to addresses assigned to each end of its VRF interfaces.

- 将T2附加到分配给其VRF接口两端的地址。

If a particular VRF interface attaches to the SP's network management system, then that VRF is configured to attach T1 to the address of that system, and to import routes that have T2 attached to them.


13. Security Considerations
13. 安全考虑
13.1. Data Plane
13.1. 数据平面

By security in the "data plane", we mean protection against the following possibilities:


- Packets from within a VPN travel to a site outside the VPN, other than in a manner consistent with the policies of the VPN.

- 来自VPN内的数据包以与VPN策略一致的方式以外的方式传输到VPN外的站点。

- Packets from outside a VPN enter one of the VPN's sites, other than in a manner consistent with the policies of the VPN.

- 来自VPN外部的数据包进入VPN的一个站点,而不是以与VPN策略一致的方式。

Under the following conditions:


1. a backbone router does not accept labeled packets over a particular data link, unless it is known that that data link attaches only to trusted systems, or unless it is known that such packets will leave the backbone before the IP header or any labels lower in the stack will be inspected, and

1. 主干路由器不接受特定数据链路上的标记数据包,除非已知该数据链路仅连接到受信任的系统,或者已知此类数据包将在检查IP报头或堆栈中较低的任何标签之前离开主干,以及

2. labeled VPN-IPv4 routes are not accepted from untrusted or unreliable routing peers,

2. 不接受来自不受信任或不可靠路由对等方的标记VPN-IPv4路由,

3. no successful attacks have been mounted on the control plane,

3. 控制飞机上没有成功的攻击,

the data plane security provided by this architecture is virtually identical to that provided to VPNs by Frame Relay or ATM backbones. If the devices under the control of the SP are properly configured, data will not enter or leave a VPN unless authorized to do so.


Condition 1 above can be stated more precisely. One should discard a labeled packet received from a particular neighbor unless one of the following two conditions holds:


- the packet's top label has a label value that the receiving system has distributed to that neighbor, or

- 数据包的顶部标签具有接收系统已分发给该邻居的标签值,或

- the packet's top label has a label value that the receiving system has distributed to a system beyond that neighbor (i.e., when it is known that the path from the system to which the label was distributed to the receiving system may be via that neighbor).

- 数据包的顶部标签具有接收系统已分配给该邻居之外的系统的标签值(即,当知道从标签分配给接收系统的系统的路径可能通过该邻居时)。

Condition 2 above is of most interest in the case of inter-provider VPNs (see Section 10). For inter-provider VPNs constructed according to scheme b) of Section 10, condition 2 is easily checked. (The issue of security when scheme (c) of Section 10 is used is for further study.)


It is worth noting that the use of MPLS makes it much simpler to provide data plane security than might be possible if one attempted to use some form of IP tunneling in place of the MPLS outer label. It is a simple matter to have one's border routers refuse to accept a labeled packet unless the first of the above conditions applies to it. It is rather more difficult to configure a router to refuse to accept an IP packet if that packet is an IP tunneled packet whose destination address is that of a PE router; certainly, this is not impossible to do, but it has both management and performance implications.


MPLS-in-IP and MPLS-in-GRE tunneling are specified in [MPLS-in-IP-GRE]. If it is desired to use such tunnels to carry VPN packets, then the security considerations described in Section 8 of that document must be fully understood. Any implementation of BGP/MPLS IP VPNs that allows VPN packets to be tunneled as described in that document MUST contain an implementation of IPsec that can be used as therein described. If the tunnel is not secured by IPsec, then the technique of IP address filtering at the border routers, described in Section 8.2 of that document, is the only means of ensuring that a packet that exits the tunnel at a particular egress PE was actually placed in the tunnel by the proper tunnel head node (i.e., that the packet does not have a spoofed source address). Since border routers frequently filter only source addresses, packet filtering may not be effective unless the egress PE can check the IP source address of any tunneled packet it receives, and compare it to a list of IP addresses that are valid tunnel head addresses. Any implementation that allows MPLS-in-IP and/or MPLS-in-GRE tunneling to be used without IPsec MUST allow the egress PE to validate in this manner the IP source address of any tunneled packet that it receives.

[MPLS in IP GRE]中指定了IP中的MPLS和GRE隧道中的MPLS。如果希望使用此类隧道来承载VPN数据包,则必须充分理解该文件第8节中描述的安全注意事项。BGP/MPLS IP VPN的任何实现,如果允许按照该文档中所述对VPN数据包进行隧道传输,则必须包含可按照其中所述使用的IPsec实现。如果隧道不受IPsec保护,则该文件第8.2节所述的边界路由器IP地址过滤技术是确保在特定出口PE处退出隧道的数据包由适当的隧道头节点实际放置在隧道中的唯一方法(即,数据包没有伪造的源地址)。由于边界路由器经常只过滤源地址,除非出口PE能够检查其接收的任何隧道数据包的IP源地址,并将其与有效隧道头地址的IP地址列表进行比较,否则数据包过滤可能无效。允许IP中的MPLS和/或GRE隧道中的MPLS的任何实现都是有效的没有IPsec的ed必须允许出口PE以这种方式验证其接收的任何隧道数据包的IP源地址。

In the case where a number of CE routers attach to a PE router via a LAN interface, to ensure proper security, one of the following conditions must hold:


1. All the CE routers on the LAN belong to the same VPN, or

1. LAN上的所有CE路由器属于同一VPN,或

2. A trusted and secured LAN switch divides the LAN into multiple VLANs, with each VLAN containing only systems of a single VPN; in this case, the switch will attach the appropriate VLAN tag to any packet before forwarding it to the PE router.

2. 受信任和安全的LAN交换机将LAN划分为多个VLAN,每个VLAN仅包含单个VPN的系统;在这种情况下,交换机将在将数据包转发到PE路由器之前,将适当的VLAN标记附加到任何数据包。

Cryptographic privacy is not provided by this architecture, nor by Frame Relay or ATM VPNs. These architectures are all compatible with the use of cryptography on a CE-CE basis, if that is desired.

该体系结构、帧中继或ATM VPN均不提供加密隐私。如果需要的话,这些体系结构都与CE-CE基础上的加密技术的使用兼容。

The use of cryptography on a PE-PE basis is for further study.


13.2. Control Plane
13.2. 控制平面

The data plane security of the previous section depends on the security of the control plane. To ensure security, neither BGP nor LDP connections should be made with untrusted peers. The TCP/IP MD5 authentication option [TCP-MD5] should be used with both these protocols. The routing protocol within the SP's network should also be secured in a similar manner.

上一节的数据平面安全性取决于控制平面的安全性。为确保安全性,BGP和LDP连接均不应与不受信任的对等方建立。TCP/IP MD5身份验证选项[TCP-MD5]应与这两个协议一起使用。SP网络中的路由协议也应以类似方式进行保护。

13.3. Security of P and PE Devices
13.3. P和PE设备的安全性

If the physical security of these devices is compromised, data plane security may also be compromised.


The usual steps should be taken to ensure that IP traffic from the public Internet cannot be used to modify the configuration of these devices, or to mount Denial of Service attacks on them.


14. Quality of Service
14. 服务质量

Although not the focus of this paper, Quality of Service is a key component of any VPN service. In MPLS/BGP VPNs, existing L3 QoS capabilities can be applied to labeled packets through the use of the "experimental" bits in the shim header [MPLS-ENCAPS], or, where ATM is used as the backbone, through the use of ATM QoS capabilities. The traffic engineering work discussed in [MPLS-RSVP] is also directly applicable to MPLS/BGP VPNs. Traffic engineering could even be used to establish label switched paths with particular QoS characteristics between particular pairs of sites, if that is desirable. Where an MPLS/BGP VPN spans multiple SPs, the architecture described in [PASTE] may be useful. An SP may apply either intserv (Integrated Services) or diffserv (Differentiated Services) capabilities to a particular VPN, as appropriate.

虽然不是本文的重点,但服务质量是任何VPN服务的关键组成部分。在MPLS/BGP VPN中,现有的L3 QoS功能可通过使用垫片头[MPLS-ENCAPS]中的“实验”位,或在ATM用作主干的情况下,通过使用ATM QoS功能,应用于标记的数据包。[MPLS-RSVP]中讨论的流量工程工作也直接适用于MPLS/BGP VPN。如果需要的话,流量工程甚至可以用于在特定站点对之间建立具有特定QoS特征的标签交换路径。如果MPLS/BGP VPN跨越多个SP,[PASTE]中描述的体系结构可能有用。SP可以对特定VPN应用intserv(集成服务)或diffserv(区分服务)功能(视情况而定)。

15. Scalability
15. 可伸缩性

We have discussed scalability issues throughout this paper. In this section, we briefly summarize the main characteristics of our model with respect to scalability.


The Service Provider backbone network consists of (a) PE routers, (b) BGP Route Reflectors, (c) P routers (that are neither PE routers nor Route Reflectors), and, in the case of multi-provider VPNs, (d) ASBRs.


P routers do not maintain any VPN routes. In order to properly forward VPN traffic, the P routers need only maintain routes to the PE routers and the ASBRs. The use of two levels of labeling is what makes it possible to keep the VPN routes out of the P routers.


A PE router maintains VPN routes, but only for those VPNs to which it is directly attached.


Route reflectors can be partitioned among VPNs so that each partition carries routes for only a subset of the VPNs supported by the Service Provider. Thus, no single route reflector is required to maintain routes for all VPNs.


For inter-provider VPNs, if the ASBRs maintain and distribute VPN-IPv4 routes, then the ASBRs can be partitioned among VPNs in a similar manner, with the result that no single ASBR is required to maintain routes for all the inter-provider VPNs. If multi-hop EBGP is used, then the ASBRs need not maintain and distribute VPN-IPv4 routes at all.


As a result, no single component within the Service Provider network has to maintain all the routes for all the VPNs. So the total capacity of the network to support increasing numbers of VPNs is not limited by the capacity of any individual component.


16. IANA Considerations
16. IANA考虑

The Internet Assigned Numbers Authority (IANA) has created a new registry for the "Route Distinguisher Type Field" (see Section 4.2). This is a two-byte field. Types 0, 1, and 2 are defined by this document. Additional Route Distinguisher Type Field values with a high-order bit of 0 may be allocated by IANA on a "First Come, First Served" basis [IANA]. Values with a high-order bit of 1 may be allocated by IANA based on "IETF consensus" [IANA].


This document specifies (see Section 4.3.4) the use of the BGP Address Family Identifier (AFI) value 1, along with the BGP Subsequent Address Family Identifier (SAFI) value 128, to represent the address family "VPN-IPv4 Labeled Addresses", which is defined in this document.


The use of AFI value 1 for IP is as currently specified in the IANA registry "Address Family Identifier", so IANA need take no action with respect to it.


The SAFI value 128 was originally specified as "Private Use" in the IANA "Subsequent Address Family Identifier" registry. IANA has changed the SAFI value 128 from "private use" to "MPLS-labeled VPN address".


17. Acknowledgements
17. 致谢

The full list of contributors can be found in Section 18.


Significant contributions to this work have also been made by Ravi Chandra, Dan Tappan, and Bob Thomas.


We also wish to thank Shantam Biswas for his review and contributions.

我们还要感谢Shantam Biswas的审查和贡献。

18. Contributors
18. 贡献者

Tony Bogovic Telcordia Technologies 445 South Street, Room 1A264B Morristown, NJ 07960

新泽西州莫里斯镇南大街445号1A264B室Tony Bogovic Telcordia Technologies 07960


Stephen John Brannon Swisscom AG Postfach 1570 CH-8301 Glattzentrum (Zuerich), Switzerland

Stephen John Brannon Swisscom AG Postfach 1570 CH-8301 Glattzentrum,瑞士


Marco Carugi Nortel Networks S.A. Parc d'activites de Magny-Les Jeunes Bois CHATEAUFORT 78928 YVELINES Cedex 9 - FRANCE

Marco Carugi Nortel Networks S.A.马尼-莱斯-琼斯-博伊斯城堡活动公园78928伊夫林-塞德克斯9号-法国


Christopher J. Chase AT&T 200 Laurel Ave Middletown, NJ 07748 USA



Ting Wo Chung Bell Nexxia 181 Bay Street Suite 350 Toronto, Ontario M5J2T3



Eric Dean


Jeremy De Clercq Alcatel Network Strategy Group Francis Wellesplein 1 2018 Antwerp, Belgium

Jeremy De Clercq阿尔卡特网络战略集团Francis Wellesplein 1 2018比利时安特卫普


Luyuan Fang AT&T IP Backbone Architecture 200 Laurel Ave. Middletown, NJ 07748



Paul Hitchen BT BT Adastral Park Martlesham Heath, Ipswich IP5 3RE UK

Paul Hitchen BT BT Adastral Park Martlesham Heath,英国伊普斯维奇IP5 3RE


Manoj Leelanivas Juniper Networks, Inc. 385 Ravendale Drive Mountain View, CA 94043 USA

Manoj Leelanivas Juniper Networks,Inc.美国加利福尼亚州拉文代尔山景大道385号,邮编94043


Dave Marshall Worldcom 901 International Parkway Richardson, Texas 75081



Luca Martini Cisco Systems, Inc. 9155 East Nichols Avenue, Suite 400 Englewood, CO, 80112



Monique Jeanne Morrow Cisco Systems, Inc. Glatt-com, 2nd floor CH-8301 Glattzentrum, Switzerland

Monique Jeanne Morrow Cisco Systems,Inc.瑞士格拉茨岑特鲁姆CH-8301二楼格拉特公司


Ravichander Vaidyanathan Telcordia Technologies 445 South Street, Room 1C258B Morristown, NJ 07960

Ravichander Vaidyanathan Telcordia Technologies新泽西州莫里斯镇南大街445号1C258B室07960


Adrian Smith BT BT Adastral Park Martlesham Heath, Ipswich IP5 3RE UK

阿德里安·史密斯英国电信公司阿达斯特拉尔公园马特勒沙姆希思,英国伊普斯威奇IP5 3RE


Vijay Srinivasan 1200 Bridge Parkway Redwood City, CA 94065



Alain Vedrenne Equant Heraklion, 1041 route des Dolines, BP347 06906 Sophia Antipolis, Cedex, France

法国塞德克斯索菲亚安提波利斯,BP347 06906,多林路1041号,阿兰·韦德伦·埃坎特·赫拉克利翁

19. Normative References
19. 规范性引用文件

[BGP] Rekhter, Y. and T. Li, "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, January 2006.

[BGP]Rekhter,Y.和T.Li,“边境网关协议4(BGP-4)”,RFC 42712006年1月。

[BGP-MP] Bates, T., Rekhter, Y., Chandra, R., and D. Katz, "Multiprotocol Extensions for BGP-4", RFC 2858, June 2000.

[BGP-MP]Bates,T.,Rekhter,Y.,Chandra,R.,和D.Katz,“BGP-4的多协议扩展”,RFC 28582000年6月。

[BGP-EXTCOMM] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended Communities Attribute", RFC 4360, February 2006.

[BGP-EXTCOMM]Sangli,S.,Tappan,D.,和Y.Rekhter,“BGP扩展社区属性”,RFC 4360,2006年2月。

[MPLS-ARCH] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, January 2001.

[MPLS-ARCH]Rosen,E.,Viswanathan,A.,和R.Callon,“多协议标签交换体系结构”,RFC 30312001年1月。

[MPLS-BGP] Rekhter, Y. and E. Rosen, "Carrying Label Information in BGP-4", RFC 3107, May 2001.

[MPLS-BGP]Rekhter,Y.和E.Rosen,“在BGP-4中携带标签信息”,RFC 3107,2001年5月。

[MPLS-ENCAPS] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack Encoding", RFC 3032, January 2001.

[MPLS-ENCAPS]Rosen,E.,Tappan,D.,Fedorkow,G.,Rekhter,Y.,Farinaci,D.,Li,T.,和A.Conta,“MPLS标签堆栈编码”,RFC 3032,2001年1月。

20. Informative References
20. 资料性引用

[BGP-AS4] Vohra, Q. and E. Chen, "BGP Support for Four-Octet AS Number Space", Work in Progress, March 2004.


[BGP-ORF] Chen, E. and Y. Rekhter, "Cooperative Route Filtering Capability for BGP-4", Work in Progress, March 2004.


[BGP-RFSH] Chen, E., "Route Refresh Capability for BGP-4", RFC 2918, September 2000.

[BGP-RFSH]Chen,E.“BGP-4的路由刷新能力”,RFC 2918,2000年9月。

[BGP-RR] Bates, T., Chandra, R., and E. Chen, "BGP Route Reflection - An Alternative to Full Mesh IBGP", RFC 2796, April 2000.

[BGP-RR]Bates,T.,Chandra,R.,和E.Chen,“BGP路由反射-全网格IBGP的替代方案”,RFC 2796,2000年4月。

[IANA] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.

[IANA]Narten,T.和H.Alvestrand,“在RFCs中编写IANA注意事项部分的指南”,BCP 26,RFC 2434,1998年10月。

[MPLS-ATM] Davie, B., Lawrence, J., McCloghrie, K., Rosen, E., Swallow, G., Rekhter, Y., and P. Doolan, "MPLS using LDP and ATM VC Switching", RFC 3035, January 2001.

[MPLS-ATM]Davie,B.,Lawrence,J.,McCloghrie,K.,Rosen,E.,Swallow,G.,Rekhter,Y.,和P.Doolan,“使用LDP和ATM VC交换的MPLS”,RFC 3035,2001年1月。

[MPLS/BGP-IPsec] Rosen, E., De Clercq, J., Paridaens, O., T'Joens, Y., and C. Sargor, "Architecture for the Use of PE-PE IPsec Tunnels in BGP/MPLS IP VPNs", Work in Progress, March 2004.

[MPLS/BGP IPsec]Rosen,E.,De Clercq,J.,Paridaens,O.,T'Joens,Y.,和C.Sargor,“在BGP/MPLS IP VPN中使用PE-PE IPsec隧道的体系结构”,正在进行的工作,2004年3月。

[MPLS-FR] Conta, A., Doolan, P., and A. Malis, "Use of Label Switching on Frame Relay Networks Specification", RFC 3034, January 2001.

[MPLS-FR]Conta,A.,Doolan,P.,和A.Malis,“帧中继网络上标签切换的使用规范”,RFC 3034,2001年1月。

[MPLS-in-IP-GRE] Worster, T., Rekhter, Y., and E. Rosen, "Encapsulating MPLS in IP or Generic Routing Encapsulation (GRE)", RFC 4023, March 2005.

[IP GRE中的MPLS]Worster,T.,Rekhter,Y.,和E.Rosen,“在IP中封装MPLS或通用路由封装(GRE)”,RFC 4023,2005年3月。

[MPLS-LDP] Andersson, L., Doolan, P., Feldman, N., Fredette, A., and B. Thomas, "LDP Specification", RFC 3036, January 2001.

[MPLS-LDP]Andersson,L.,Doolan,P.,Feldman,N.,Fredette,A.,和B.Thomas,“LDP规范”,RFC 3036,2001年1月。

[MPLS-RSVP] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, December 2001.

[MPLS-RSVP]Awduche,D.,Berger,L.,Gan,D.,Li,T.,Srinivasan,V.,和G.Swallow,“RSVP-TE:LSP隧道RSVP的扩展”,RFC 3209,2001年12月。

[OSPFv2] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.

[OSPFv2]Moy,J.,“OSPF版本2”,STD 54,RFC 23281998年4月。

[PASTE] Li, T. and Y. Rekhter, "A Provider Architecture for Differentiated Services and Traffic Engineering (PASTE)", RFC 2430, October 1998.

[PASTE]Li,T.和Y.Rekhter,“差异化服务和流量工程的提供商架构(PASTE)”,RFC 2430,1998年10月。

[RIP] Malkin, G., "RIP Version 2", STD 56, RFC 2453, November 1998.

[RIP]Malkin,G.,“RIP版本2”,STD 56,RFC 2453,1998年11月。

[OSPF-2547-DNBIT] Rosen, E., Psenak, P., and P. Pillay-Esnault, "Using an LSA Options Bit to Prevent Looping in BGP/MPLS IP VPNs", Work in Progress, March 2004.

[OSPF-2547-DNBIT]Rosen,E.,Psenak,P.,和P.Pillay Esnault,“使用LSA选项位防止BGP/MPLS IP VPN中的循环”,正在进行的工作,2004年3月。

[TCP-MD5] Heffernan, A., "Protection of BGP Sessions via the TCP MD5 Signature Option", RFC 2385, August 1998.

[TCP-MD5]Heffernan,A.,“通过TCP MD5签名选项保护BGP会话”,RFC 2385,1998年8月。

[VPN-MCAST] Rosen, E., Cai, Y., and J. Wijsnands, "Multicast in MPLS/BGP VPNs", Work in Progress, May 2004.

[VPN-MCAST]Rosen,E.,Cai,Y.,和J.Wijsnands,“MPLS/BGP VPN中的多播”,正在进行的工作,2004年5月。

[VPN-OSPF] Rosen, E., Psenak, P., and P. Pillay-Esnault, "OSPF as the PE/CE Protocol in BGP/MPLS VPNs", Work in Progress, February 2004.

[VPN-OSPF]Rosen,E.,Psenak,P.,和P.Pillay Esnault,“OSPF作为BGP/MPLS VPN中的PE/CE协议”,正在进行的工作,2004年2月。

Authors' Addresses


Eric C. Rosen Cisco Systems, Inc. 1414 Massachusetts Avenue Boxborough, MA 01719

Eric C.Rosen Cisco Systems,Inc.马萨诸塞州伯斯堡马萨诸塞大道1414号,邮编01719


Yakov Rekhter Juniper Networks 1194 N. Mathilda Avenue Sunnyvale, CA 94089



Full Copyright Statement


Copyright (C) The Internet Society (2006).


This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights.

本文件受BCP 78中包含的权利、许可和限制的约束,除其中规定外,作者保留其所有权利。



Intellectual Property


The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79.

IETF对可能声称与本文件所述技术的实施或使用有关的任何知识产权或其他权利的有效性或范围,或此类权利下的任何许可可能或可能不可用的程度,不采取任何立场;它也不表示它已作出任何独立努力来确定任何此类权利。有关RFC文件中权利的程序信息,请参见BCP 78和BCP 79。

Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at


The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at




Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA).