Network Working Group B. Jamoussi
Request for Comments: 2340 D. Jamieson
Category: Informational D. Williston
S. Gabe
Nortel (Northern Telecom) Ltd.
May 1998
Network Working Group B. Jamoussi
Request for Comments: 2340 D. Jamieson
Category: Informational D. Williston
S. Gabe
Nortel (Northern Telecom) Ltd.
May 1998
Nortel's Virtual Network Switching (VNS) Overview
北电虚拟网络交换（VNS）概述
Status of this Memo
本备忘录的状况
This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.
本备忘录为互联网社区提供信息。它没有规定任何类型的互联网标准。本备忘录的分发不受限制。
Copyright Notice
版权公告
Copyright (C) The Internet Society (1998). All Rights Reserved.
版权所有（C）互联网协会（1998年）。版权所有。
Abstract
摘要
This document provides an overview of Virtual Network Switching (VNS).
本文档概述了虚拟网络交换（VNS）。
VNS is a multi-protocol switching architecture that provides COS-sensitive packet switching, reduces the complexity of operating protocols like PPP and frame relay, provides logical networks and traffic segregation for Virtual Private Networks (VPNs), security and traffic engineering, enables efficient WAN broadcasting and multicasting, and reduces address space requirements. VNS reduces the number of routing hops over the WAN by switching packets based on labels.
VNS是一种多协议交换体系结构，提供对COS敏感的分组交换，降低PPP和帧中继等操作协议的复杂性，为虚拟专用网络（VPN）提供逻辑网络和流量隔离，提供安全和流量工程，实现高效WAN广播和多播，并减少了地址空间需求。VNS通过基于标签交换数据包来减少WAN上的路由跳数。
VNS has been proven in production networks for several years.
多年来，VNS已在生产网络中得到验证。
Table of Contents
目录
1 Introduction ............................................ 2
2 What is VNS? ............................................ 3
3 VNS Header ............................................. 5
4 VNS Label Distribution .................................. 7
5 Logical Networks (LNs) .................................... 7
6 VNS Routing ............................................. 8
7 VNS Forwarding .......................................... 9
7.1 Unicast ................................................ 9
7.2 Multicast .............................................. 9
8 Traffic Engineering ..................................... 10
1 Introduction ............................................ 2
2 What is VNS? ............................................ 3
3 VNS Header ............................................. 5
4 VNS Label Distribution .................................. 7
5 Logical Networks (LNs) .................................... 7
6 VNS Routing ............................................. 8
7 VNS Forwarding .......................................... 9
7.1 Unicast ................................................ 9
7.2 Multicast .............................................. 9
8 Traffic Engineering ..................................... 10
8.1 Equal Cost Multipaths .................................. 10
8.2 Trunk Load Spreading ................................... 10
9 Class of Service ........................................ 11
10 VNS Migration Strategies ................................ 11
11 Summary ................................................. 11
12 Security Considerations ................................. 12
13 Acknowledgments ......................................... 12
14 Authors' Addresses ...................................... 13
15 Full Copyright Statement ................................ 14
8.1 Equal Cost Multipaths .................................. 10
8.2 Trunk Load Spreading ................................... 10
9 Class of Service ........................................ 11
10 VNS Migration Strategies ................................ 11
11 Summary ................................................. 11
12 Security Considerations ................................. 12
13 Acknowledgments ......................................... 12
14 Authors' Addresses ...................................... 13
15 Full Copyright Statement ................................ 14
There are several key problem areas with today's wide area backbone networks that carry LAN traffic: scalability, service differentiation, redundancy, administration, and traffic containment.
当今承载LAN流量的广域骨干网存在几个关键问题：可扩展性、服务差异化、冗余、管理和流量控制。
First, scalability is becoming a major concern because of the rapid growth in bandwidth demand and geographical reach. As the size of the WAN network grows traditional point-to-point and NBMA topologies or network models lose their performance.
首先，由于带宽需求和地理范围的快速增长，可扩展性正成为一个主要问题。随着广域网网络规模的增长，传统的点到点和NBMA拓扑或网络模型失去了性能。
Second, the need to provide several Classes of Service (CoS) has never been greater. The days of a single "best effort" service are over and service providers demand ways to differentiate the quality of the service offered to their clients based on several policies.
第二，提供几类服务（CoS）的需求从未如此之大。单一“尽力而为”服务的时代已经过去，服务提供商要求根据多种政策来区分为其客户提供的服务质量。
Third, the WAN is often carrying mission-critical traffic and loss of service is not acceptable. So far, path redundancy has been addressed inefficiently by requiring additional links or VCs.
第三，广域网通常承载任务关键型流量，服务丢失是不可接受的。到目前为止，由于需要额外的链路或VCs，路径冗余问题得到了低效的解决。
Fourth, network operators demand easy and simplified network administration. Large NBMA topologies require extensive PVC provisioning until SVC deployment becomes more ubiquitous. For Point-to-point models, IP address space may be used inefficiently and non-trivial network schemas are required to contain reserved address space.
第四，网络运营商要求简化网络管理。大型NBMA拓扑需要大量PVC供应，直到SVC部署变得更普遍。对于点对点模型，IP地址空间的使用效率可能会很低，并且需要非平凡的网络模式来包含保留的地址空间。
Finally, proper segregation of traffic is becoming a must. This requirement is being addressed today by adding leased lines or VCs used to separate traffic flows based on regions or interest or protocol.
最后，适当的交通隔离正成为必须。如今，通过增加用于根据区域、兴趣或协议分离流量的租用线路或VCs，这一要求得到了满足。
Nortel's Virtual Network Switching (VNS) is a technology that provides efficient solutions to these challenges.
北电的虚拟网络交换（VNS）技术为这些挑战提供了有效的解决方案。
Section 2 provides an overview of VNS. The VNS header is specified in Section 3. Section 4 describes the VNS label distribution mechanism. Section 5 defines how a VNS network can be partitioned into Logical Networks (LN). Section 6 outlines VNS routing. Section 7 defines both unicast and multicast forwarding. Section 8 describes the mechanisms used to engineer the traffic. Section 9 defines the COS based switching of VNS. Section 10 provides network migration scenarios using VNS. A summary of VNS is provided in Section 11.
第2节概述了VNS。第3节规定了VNS标头。第4节描述了VNS标签分发机制。第5节定义了如何将VNS网络划分为逻辑网络（LN）。第6节概述了VNS路由。第7节定义了单播和多播转发。第8节描述了用于设计流量的机制。第9节定义了基于COS的VN切换。第10节提供了使用VNS的网络迁移场景。第11节提供了VNS概述。
Virtual Network Switching (VNS) is a CoS-sensitive multi-protocol label switching architecture that reduces or eliminates the number of layer 3 hops over the WAN by switching traffic based on labels.
虚拟网络交换（VNS）是一种对CoS敏感的多协议标签交换体系结构，它通过基于标签交换流量来减少或消除WAN上的第3层跳数。
VNS makes a network of point to point links appear to be a single LAN (broadcast, multiple access) media. The network used by a particular instance of VNS is called a Logical Network (LN) which is described in more detail in Section 5.
VNS使点对点链接网络看起来像是一个单一的LAN（广播、多址）媒体。VNS的特定实例所使用的网络称为逻辑网络（LN），第5节将对此进行更详细的描述。
In reference to the ISO Network Layering Model, the Data Link Layer is expanded to include VNS network layer. To the ISO Network Layer, (e.g., IP), VNS is treated as a Data Link Layer.
参考ISO网络分层模型，将数据链路层扩展为包括VNS网络层。对于ISO网络层（例如IP），VNS被视为数据链路层。
------------------------
| Application |
------------------------
| Presentation |
------------------------
| Session |
------------------------
| Transport |
------------------------ -------------------------
| Network (e.g., IP) | / Network VNS |
----------------------------- |
| Data Link |--------------------------
----------------------------- |
| Physical | \ data link (e.g., ATM) |
------------------------ -------------------------
------------------------
| Application |
------------------------
| Presentation |
------------------------
| Session |
------------------------
| Transport |
------------------------ -------------------------
| Network (e.g., IP) | / Network VNS |
----------------------------- |
| Data Link |--------------------------
----------------------------- |
| Physical | \ data link (e.g., ATM) |
------------------------ -------------------------
Figure 1. ISO Network Layering Model for VNS
图1。VNS的ISO网络分层模型
In a VNS Network, three separate nodal functions are defined. An ingress node, an egress node, and a tandem node. The ingress and egress nodes define the boundary between an IP network and the VNS network. Therefore, these nodes run both IP routing and VNS routing. However, tandem nodes need only run VNS routing.
在VNS网络中，定义了三个独立的节点函数。入口节点、出口节点和串联节点。入口和出口节点定义了IP网络和VNS网络之间的边界。因此，这些节点同时运行IP路由和VNS路由。然而，串联节点只需要运行VNS路由。
A LAN packet is encapsulated in a VNS header as it enters the LN. The label in the header is used to switch the packet across the LN. The encapsulation header contains the identifier of the last node (or egress node) that processes the packet as it traverses the LN. It is the first node (or ingress node) that decides to which egress node the packet is sent. All nodes between the ingress and egress nodes (known as tandem nodes) decide independently the best packet forwarding route to the egress node identified in the packet.
LAN数据包在进入LN时封装在VNS报头中。标头中的标签用于在LN之间切换数据包。封装头包含最后一个节点（或出口节点）的标识符，该节点在数据包穿过LN时处理数据包。第一个节点（或入口节点）决定将数据包发送到哪个出口节点。入口和出口节点之间的所有节点（称为串联节点）独立地决定到分组中标识的出口节点的最佳分组转发路由。
The network layer protocols view VNS as a shared broadcast media, where the speed to reach any node on the media is the same for all nodes. VNS ensures that traffic destined to other nodes is forwarded optimally. This transparent view of the VNS means that all the details of the network (for example, topology and link states) can be hidden from the Upper Layer Protocols (e.g. Layer 3 routing protocols) and their applications. VNS also ensures that changes to topology and link state are hidden.
网络层协议将VNS视为共享广播媒体，其中到达媒体上任何节点的速度对于所有节点都是相同的。VNS确保目的地为其他节点的流量以最佳方式转发。VNS的这种透明视图意味着可以对上层协议（例如，第3层路由协议）及其应用隐藏网络的所有细节（例如，拓扑和链路状态）。VNS还确保对拓扑和链路状态的更改被隐藏。
The network layer protocol on the ingress node views the network layer protocol on the egress node as its logical and directly connected neighbor. This is significant because the network layer protocols always decide which directly connected neighbor should receive a forwarded packet. The details of the actual topology supporting the connectionless network are managed entirely by the Virtual Network Switching and are hidden from the network layer protocols. To the network layer, VNS simply appears to be another Data Link Layer (or media), even though VNS is a network layer itself running on top of the actual Data Link Layer (for example, ATM trunks).
入口节点上的网络层协议将出口节点上的网络层协议视为其逻辑和直接连接的邻居。这很重要，因为网络层协议总是决定哪个直接连接的邻居应该接收转发的数据包。支持无连接网络的实际拓扑的细节完全由虚拟网络交换管理，并且对网络层协议隐藏。对于网络层来说，VNS仅仅是另一个数据链路层（或媒体），即使VNS本身是一个运行在实际数据链路层（例如ATM中继）之上的网络层。
For the ingress node to choose the egress node that provides the best path to the packet's final destination, it must have knowledge of the following:
为了让入口节点选择提供到数据包最终目的地的最佳路径的出口节点，它必须具备以下知识：
- the nodes that can be reached in the network - the topology of the network that is using the VNS services for transport across the network (but not necessarily the topology of the full network)
- 网络中可以到达的节点-使用VNS服务在网络上传输的网络拓扑（但不一定是整个网络的拓扑）
This knowledge is obtained through the network layer routing mechanisms such as, IP's Open Shortest Path First (OSPF) and Address Resolution Protocol (ARP).
这些知识是通过网络层路由机制获得的，如IP的开放最短路径优先（OSPF）和地址解析协议（ARP）。
Once the network layer protocol on the ingress node has decided which neighbor to transmit the packet to, it is the responsibility of VNS forwarding, a part of VNS, to deliver the packet to that node. Once the packet arrives at the egress node, the packet is delivered to the network layer protocol, which then forwards it to its ultimate
一旦入口节点上的网络层协议决定将数据包发送到哪个邻居，则VNS转发（VNS的一部分）负责将数据包发送到该节点。一旦数据包到达出口节点，数据包就被传送到网络层协议，然后网络层协议将数据包转发到其最终节点
destination.
目的地
Tandem nodes have no interaction with the network layer protocols. They only require knowledge of the VNS network topology. They make their packet forwarding decision on the egress node identifier and LN identifier carried in the VNS header of the packet.
串联节点与网络层协议没有交互。它们只需要了解VNS网络拓扑。它们根据包的VNS报头中携带的出口节点标识符和LN标识符做出包转发决策。
VNS defines a unicast header shown in Figure 2 and a multicast header shown in Figure 3.
VNS定义了图2所示的单播头和图3所示的多播头。
3 2 1 0
1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTL | LNN |x|LS-Key |x|DP | CmnHdr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol Type | Destination Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| COS |x x x x| Source Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Layer Header (e.g. IP) |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3 2 1 0
1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTL | LNN |x|LS-Key |x|DP | CmnHdr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol Type | Destination Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| COS |x x x x| Source Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Layer Header (e.g. IP) |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2. Unicast VNS Header
图2。单播VNS报头
The unicast header includes the following fields:
单播标头包括以下字段：
- Common Header (CmnHdr): The common header identifies the packet to be a VNS encapsulated packet.
- 公共报头（CmnHdr）：公共报头将数据包标识为VNS封装的数据包。
- Discard Priority: Indicates the level of congestion at which the packet should be discarded. The value of this field is assigned on the originating node based on policy information (see Section 9).
- 丢弃优先级：指示应丢弃数据包的拥塞级别。该字段的值根据策略信息在发起节点上分配（参见第9节）。
- Load Spreading Key: indicates the stream to which the packet belongs for the purposes of equal cost multipath and trunk load spreading (see Section 8).
- 负载扩展键：指示数据包所属的流，以实现等成本多路径和中继负载扩展（参见第8节）。
- LNN: The Logical Network Number defines the logical network the packet belongs to. This field in is used in conjunction with the destination node identifier as the VNS switching label (see Section 5).
- LNN：逻辑网络号定义数据包所属的逻辑网络。中的该字段与目标节点标识符一起用作VNS交换标签（参见第5节）。
- TTL: The Time To Live field is used to detect and discard packets caught in temporary routing loops.
- TTL：生存时间字段用于检测和丢弃临时路由循环中捕获的数据包。
- Destination Node Identifier: This field contains an ID which uniquely identifies the destination node. This ID is unique to the physical network not just the LN. In conjunction with the LNN, this forms a global VNS switching label.
- 目标节点标识符：此字段包含唯一标识目标节点的ID。此ID是物理网络的唯一ID，而不仅仅是LN。与LNN一起，形成一个全局VNS交换标签。
- Protocol Type: indicates the type of Network layer protocol being carried in the packet. Examples include IP, IPX, and Bridging. If the packet is a multicast packet then this is indicated in this field.
- 协议类型：表示数据包中承载的网络层协议的类型。示例包括IP、IPX和桥接。如果该数据包是多播数据包，则在该字段中指明。
- Source Node Identifier: This field contains an ID which uniquely identifies the source node (ingress node).
- 源节点标识符：此字段包含唯一标识源节点（入口节点）的ID。
- CoS: The Class of Service field is used to provide routing class of service. The COS field also affects the Emission Priority of the packet in the scheduler (see Section 9).
- CoS：服务类别字段用于提供路由服务类别。COS字段还影响调度器中数据包的发射优先级（参见第9节）。
- Reserved Fields: All the fields marked with "x" are Reserved.
- 保留字段：所有标有“x”的字段均保留。
3 2 1 0
1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTL | LNN |x|LS-Key |x|DP | CmnHdr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PT = Multicast| Destination Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| COS |x x x x| Source Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol Type |x x x x x x x x| Multicast Group |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Layer Header (e.g. IP) |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Data /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3 2 1 0
1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTL | LNN |x|LS-Key |x|DP | CmnHdr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PT = Multicast| Destination Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| COS |x x x x| Source Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol Type |x x x x x x x x| Multicast Group |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Layer Header (e.g. IP) |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Data /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3. Multicast VNS Header
图3。多播VNS报头
The multicast header shown in Figure 3, includes all the fields of the unicast header. In addition, the multicast header includes the following fields:
图3所示的多播报头包括单播报头的所有字段。此外，多播标头还包括以下字段：
- Multicast Group: this field is used to identify a sub-group within the logical network that receives the multicast packets.
- 多播组：此字段用于标识逻辑网络中接收多播数据包的子组。
- Protocol Type: indicates the type of Network layer protocol being carried in the packet. Examples include IP, IPX, and Bridging.
- 协议类型：表示数据包中承载的网络层协议的类型。示例包括IP、IPX和桥接。
Label distribution in VNS is based on a distributed serverless topology driven approach. Standard ARP or address gleaning is used to distribute and map network layer addresses to VNS addresses.
VNS中的标签分发基于分布式无服务器拓扑驱动方法。标准ARP或地址收集用于分发网络层地址并将其映射到VNS地址。
A VNS Label is an 6 byte encoding of the LNN and the node ID. VNS Labels are treated as MAC addresses by the network layer. This means that labels are distributed by the same means network layers use to distribute MAC addresses. Thus, VNS leverages existing L2/L3 mapping techniques and doesn't require a separate Label Distribution Protocol.
VNS标签是LNN和节点ID的6字节编码。网络层将VNS标签视为MAC地址。这意味着标签的分发方式与网络层用于分发MAC地址的方式相同。因此，VNS利用现有的L2/L3映射技术，不需要单独的标签分发协议。
A logical network consists of a subset of the nodes in a network together with a subset of the trunking facilities that link those nodes. Logical networks partition the network into subnetworks that serve a subset of the overall topology.
逻辑网络由网络中的节点子集和连接这些节点的中继设施子集组成。逻辑网络将网络划分为子网络，这些子网络服务于整个拓扑的子集。
Each of the logical networks supported on any given node has a separate routing and forwarding table (built by VNS). Therefore, routing decisions are based on the resources available to the logical network, not the entire network.
任何给定节点上支持的每个逻辑网络都有一个单独的路由和转发表（由VNS构建）。因此，路由决策基于逻辑网络可用的资源，而不是整个网络。
Each instance of VNS will discover all the trunks which are connected to neighbors which support a matching LNN. This provides a huge administrative saving, since VNS provisioning is on a per-node basis, not on a per-link basis. VNS provisioning requires only a unique node ID and an LNN. Discovery of which trunks support which LNNs is done at run time, relieving administrative effort, and allowing the LN to dynamically adapt to topology changes.
VNS的每个实例将发现连接到支持匹配LNN的邻居的所有中继。这提供了巨大的管理节省，因为VNS配置是基于每个节点的，而不是基于每个链路的。VNS配置只需要唯一的节点ID和LNN。发现哪些中继支持哪些LNN在运行时完成，从而减轻管理工作，并允许LN动态适应拓扑更改。
Multiple Logical Networks provide the following benefits to the network system:
多个逻辑网络为网络系统提供以下好处：
- Logical networks allow service providers to service multiple private networks or (Virtual Private Internets) easily over one network.
- 逻辑网络允许服务提供商通过一个网络轻松地为多个专用网络或（虚拟专用互联网）提供服务。
- Logical networks can be used to limit the impact of one network layer protocol on the others. This is particularly true for protocols that broadcast or multicast a large percentage of either their control or data packets. This increases the effective bandwidth of the trunks and allows the overall network to scale
- 逻辑网络可用于限制一个网络层协议对其他协议的影响。对于广播或多播大部分控制或数据包的协议来说，这一点尤其正确。这增加了中继的有效带宽，并允许整个网络扩展
better.
较好的
- Logical networks allow for the configuration of the network to meet individual community of interest and geographical subnetworking needs.
- 逻辑网络允许对网络进行配置，以满足感兴趣的单个社区和地理子网络的需求。
- Routing control traffic has significance only in the local subnetwork that is isolated to that subnetwork.
- 路由控制流量仅在与该子网隔离的本地子网中具有重要意义。
- Logical networks allow different instances of the same protocol to share trunk facilities.
- 逻辑网络允许同一协议的不同实例共享中继设施。
VNS routing is a link state routing system which uses many concepts similar to OSPF and PNNI. One of the most significant departures from the others is its ability to calculate shortest path trees for routing unicast traffic and spanning trees for routing multicast traffic within a Logical Network.
VNS路由是一种链路状态路由系统，它使用了许多类似于OSPF和PNNI的概念。其中一个最重要的区别是它能够计算单播流量路由的最短路径树和逻辑网络内多播流量路由的生成树。
There is only one type of interface that VNS routing supports and this is known as a VNS link. A link is a set of trunks that join two VNS neighbor nodes. Each node in a VNS network maintains information about the state of locally attached links. This information is flooded throughout the network whenever there is a significant change to the link's state or attributes (i.e. up/down, speed change, available bandwidth change).
VNS路由只支持一种类型的接口，称为VNS链路。链路是连接两个VNS邻居节点的一组中继。VNS网络中的每个节点维护有关本地连接链路状态的信息。每当链路的状态或属性发生重大变化（即上升/下降、速度变化、可用带宽变化）时，该信息就会充斥整个网络。
Each node stores and forwards the link state information received from all other nodes. This allows each node to have the same view of all of the nodes in the network together with all of their link state information. This data is used to compute both the shortest path to reach each node in the Logical Network and a spanning tree for the Logical Network.
每个节点存储并转发从所有其他节点接收的链路状态信息。这允许每个节点具有网络中所有节点及其所有链路状态信息的相同视图。该数据用于计算到达逻辑网络中每个节点的最短路径和逻辑网络的生成树。
Logical networks are not bound to a particular trunk or link. They are configured on a node. By default, a link will support a specific logical network if the two nodes which it connects both are configured to support the logical network number. This provides a significant savings in operations over having to configure logical networks on links or trunks.
逻辑网络不绑定到特定的主干或链路。它们是在节点上配置的。默认情况下，如果链路连接的两个节点都配置为支持逻辑网络号，则链路将支持特定的逻辑网络。与必须在链路或中继上配置逻辑网络相比，这大大节省了操作成本。
When a link first comes into service, a protocol is run which allows the two neighboring nodes to exchange information about the logical networks they support. This allows the two nodes to determine if the links are to be considered as a locally attached link for a logical network.
当链路首次投入使用时，将运行一个协议，该协议允许两个相邻节点交换有关其支持的逻辑网络的信息。这允许两个节点确定链路是否被视为逻辑网络的本地连接链路。
VNS supports two types of forwarding: unicasting and multicasting. In the first type, the data packet arrives on the ingress node and unicasting forwards the data packet to a single destination (egress node). In the second type, the data packet arrives on the ingress node and multicasting forwards the data packet to all other nodes in the logical network.
VNS支持两种类型的转发：单播和多播。在第一种类型中，数据分组到达入口节点，并且单播将数据分组转发到单个目的地（出口节点）。在第二种类型中，数据包到达入口节点，并且多播将数据包转发到逻辑网络中的所有其他节点。
When a packet first enters the LAN internetwork, the network layer routing protocol determines the next hop of the best route for the packet to reach its final destination. If the best route is through a VNS Logical Network, the network layer routing protocol relies on VNS forwarding to get the packet to the egress node. A VNS packet header containing the node ID (the unique ID assigned to each node) of the egress node is added to the front of the packet and VNS forwarding is invoked to deliver the packet. The network layer routing protocol learns the egress node ID through an Address Resolution Protocol (ARP) for IP and Source Address learning for bridging.
当数据包第一次进入局域网互联网络时，网络层路由协议确定数据包到达其最终目的地的最佳路由的下一跳。如果最佳路由是通过VNS逻辑网络，则网络层路由协议依赖于VNS转发将数据包发送到出口节点。将包含出口节点的节点ID（分配给每个节点的唯一ID）的VNS分组报头添加到分组的前端，并且调用VNS转发来递送分组。网络层路由协议通过用于IP的地址解析协议（ARP）和用于桥接的源地址学习来学习出口节点ID。
As the packet traverses the LN, routing decisions are made to determine the next hop in the route to reach the destination node ID specified in the VNS header. A forwarding table is built on each node that assists in making the routing decision.
当数据包穿过LN时，会做出路由决定，以确定路由中的下一跳到达VNS报头中指定的目标节点ID。在每个节点上建立一个转发表，以帮助做出路由决策。
Each VNS instance on each node builds and maintains a forwarding table for its LN. Each forwarding table has an entry for every node that is a member of the logical network.
每个节点上的每个VNS实例为其LN构建并维护一个转发表。每个转发表都有一个作为逻辑网络成员的每个节点的条目。
In addition to the unicast forwarding function, VNS also supports a multicast forwarding service for traffic within an LN at the VNS layer. Multicast packets are delivered to all nodes supporting the logical network to which the multicast packet belongs. The packets are sent along the branches of a spanning tree that is built by each node supporting the logical network and is based on a common root node (so that each node's view of the tree is the same as other nodes). In other words, multicast packets are sent intelligently, consuming a minimum of network bandwidth. If the network topology is stable, each node receives each multicast packet only once.
除了单播转发功能外，VNS还支持VNS层LN内流量的多播转发服务。多播数据包被传送到支持多播数据包所属的逻辑网络的所有节点。数据包沿着支撑逻辑网络的每个节点构建的生成树的分支发送，生成树基于公共根节点（因此每个节点的树视图与其他节点相同）。换句话说，多播数据包是智能发送的，消耗的网络带宽最少。如果网络拓扑稳定，每个节点只接收一次多播数据包。
Multicast packets received at any node are not acknowledged. They are simply forwarded to the specified network layer interface and sent to any other neighbor nodes on the spanning tree.
在任何节点接收的多播数据包都不会得到确认。它们被简单地转发到指定的网络层接口，并发送到生成树上的任何其他邻居节点。
VNS forwarding supports two types of traffic engineering mechanisms: equal cost multipaths and trunk load spreading.
VNS转发支持两种类型的流量工程机制：等成本多路径和中继负载扩展。
Equal cost multipaths allows different streams (unique network layer source and destination address pairings) to be load spread between multiple relatively equal cost paths, through the Logical Network to the egress node.
等成本多路径允许不同的流（唯一的网络层源地址和目标地址对）在多个相对等成本路径之间进行负载分配，通过逻辑网络到出口节点。
Trunk load spreading between two neighbors can take place when multiple VNS trunks are defined between neighbors. Again, the load spreading is based on network layer streams.
当在邻居之间定义多个VNS中继时，两个邻居之间可能会发生中继负载分散。同样，负载分布基于网络层流。
From any point in a logical network, there may be multiple paths to reach a specific egress node. If VNS routing determines that more than one of these paths are of equal cost, VNS packets will be load spread between two of them.
从逻辑网络中的任何点，可能有多条路径到达特定出口节点。如果VNS路由确定这些路径中有多条具有相同的成本，则VNS数据包将在其中两条路径之间进行负载分摊。
Equal cost multipath forwarding is supported not only on ingress nodes but on tandem nodes as well. Each packet on an ingress node is tagged with an equal cost multipath key. This key is acted upon at the ingress node and stored in the VNS header to be used on tandem nodes.
不仅入口节点支持等成本多路径转发，串联节点也支持等成本多路径转发。入口节点上的每个数据包都被标记为具有相同代价的多路径密钥。该密钥在入口节点上作用，并存储在VNS报头中，以便在串联节点上使用。
The equal cost multipath key is calculated by running an algorithm over the source and destination network layer addresses. This means that, in a stable network, any given stream will always take the same path through a Logical Network avoiding the problems that misordering would otherwise cause.
通过在源和目标网络层地址上运行算法来计算等成本多路径密钥。这意味着，在一个稳定的网络中，任何给定的流在逻辑网络中总是采用相同的路径，从而避免了错误排序可能导致的问题。
VNS allows multiple trunks to be configured between neighboring VNS nodes. VNS routing considers the aggregate bandwidth of those trunks to determine the metric between the nodes. Also, VNS load spreads its traffic amongst those trunks.
VNS允许在相邻VNS节点之间配置多个中继。VNS路由考虑这些中继的总带宽，以确定节点之间的度量。此外，VNS负载将其流量分布在这些中继之间。
As is the case with equal cost multipaths, the trunk load spreading key is calculated on the ingress node from an algorithm run over the source and destination network layer addresses. The key is then stored in the VNS header to be used on all tandem nodes through the Logical Network.
与等成本多路径的情况一样，在入口节点上通过在源和目标网络层地址上运行的算法计算中继负载扩展密钥。然后，密钥存储在VNS报头中，通过逻辑网络在所有串联节点上使用。
At the ingress to a VNS Network, packets are classified according to the Class of Service (Cos) policy settings. The CoS differentiation is achieved through different Emission and Discard priorities. The semantics of the classification is carried in the VNS label (DP and COS Fields described in Section 3) to be used at the ingress node as well as all tandem points in the VNS network to affect queuing and scheduling decisions.
在进入VNS网络时，根据服务类别（Cos）策略设置对数据包进行分类。CoS区分是通过不同的排放和废弃优先级实现的。分类的语义包含在VNS标签（第3节中描述的DP和COS字段）中，用于入口节点以及VNS网络中的所有串联点，以影响排队和调度决策。
VNS supports several upper layer protocols such as IP, IPX, and Bridging. Therefore, it is a multiprotocol label switching architecture. In addition, VNS is not tied to a particular L2 technology. It runs on cell (e.g., ATM) trunks, frame trunks, or a mixture of both.
VNS支持多种上层协议，如IP、IPX和桥接。因此，它是一种多协议标签交换体系结构。此外，VNS与特定的L2技术无关。它在信元（如ATM）中继、帧中继或两者的混合上运行。
VNS can be gradually introduced in a network. It can be implemented between switching elements interconnected by point to point links. Each of the switching nodes can run layer 3 routing simultaneously with packet switching. VNS also allows for the interconnection of VNS clouds through an ATM VC.
VN可以逐渐引入网络。它可以在通过点对点链路互连的开关元件之间实现。每个交换节点可以与分组交换同时运行第3层路由。VNS还允许通过ATM VC互连VNS云。
Since VNS can run on a mixture of Frame and Cell trunks, it allows for the graceful migration of the frame links to ATM without requiring a complete immediate overhaul.
由于VNS可以在帧中继和信元中继的混合上运行，它允许帧链路优雅地迁移到ATM，而无需立即进行彻底检修。
VNS addresses scalability problems in several ways:
VNS通过几种方式解决了可伸缩性问题：
1. By a generally distributed design which doesn't require a Label Distribution Protocol, or servers of any kind. 2. By providing an efficient, distributed multicast mechanism. 3. By allowing administrators to control the size of a Logical Network, limiting traffic to a subset of the physical topology. 4. By reducing layer 3 address space/subnet requirements in the WAN which reduces the routing table size.
1. 通过不需要标签分发协议或任何类型的服务器的一般分布式设计。2.通过提供一种高效的分布式多播机制。3.通过允许管理员控制逻辑网络的大小，将流量限制为物理拓扑的一个子集。4.通过减少WAN中的第3层地址空间/子网要求，减少了路由表的大小。
VNS provides redundancy transparent to the network layer protocol by managing the network of trunks independently of the network layer. VNS will automatically discover any topology changes and re-route traffic accordingly.
VNS通过独立于网络层管理中继网络，提供对网络层协议透明的冗余。VNS将自动发现任何拓扑变化，并相应地重新路由流量。
VNS eases network administration by dynamically keeping track of which trunks are available for each LNN. Network administrators don't have to configure VNS or network layer addresses on a per link basis. Network layer addresses only have to be assigned on a per Logical Network basis. For nodes which will only be tandem VNS nodes, network layer addresses aren't required at all.
VNS通过动态跟踪每个LNN可用的中继，简化了网络管理。网络管理员不必基于每条链路配置VNS或网络层地址。网络层地址只需按每个逻辑网络分配。对于仅为串联VNS节点的节点，根本不需要网络层地址。
Since VNS traffic is constrained within an LNN, administrators have control of where VNS traffic is allowed to flow.
由于VNS流量在LNN内受到限制，管理员可以控制允许VNS流量流动的位置。
Finally, VNS supports switching of several Upper Layer Protocols and supports several media (cell and Frame) or a mixture thereof. Switching in the core of the WAN removes the need for routers and improves the performance due to a reduction in the number of fields that need to processed.
最后，VNS支持若干上层协议的交换，并支持若干媒体（小区和帧）或其混合。WAN核心中的交换消除了对路由器的需求，并由于需要处理的字段数量减少而提高了性能。
Logical networks provide a means of restricting traffic flow for security purposes. VNS also relies on the inherent security of the L2 media such as an ATM Virtual Circuit.
出于安全目的，逻辑网络提供了一种限制流量的方法。VNS还依赖于L2媒体的固有安全性，如ATM虚拟电路。
The authors would like to acknowledge the valuable comments of Terry Boland, Pierre Cousineau, Robert Eros, Robert Tomkins, and John Whatman.
作者要感谢Terry Boland、Pierre Cousineau、Robert Eros、Robert Tomkins和John Whatman的宝贵评论。
Bilel Jamoussi Nortel (Northern Telecom), Ltd. PO Box 3511 Station C Ottawa ON K1Y 4H7 Canada
加拿大K1Y 4H7渥太华C站3511号邮政信箱Bilel Jamoussi Nortel（北方电信）有限公司
EMail: jamoussi@Nortel.ca
EMail: jamoussi@Nortel.ca
Dwight Jamieson Nortel (Northern Telecom), Ltd. PO Box 3511 Station C Ottawa ON K1Y 4H7 Canada
Dwight Jamieson Nortel（北方电信）有限公司加拿大K1Y 4H7渥太华C站3511号邮政信箱
EMail: djamies@Nortel.ca
EMail: djamies@Nortel.ca
Dan Williston Nortel (Northern Telecom), Ltd. PO Box 3511 Station C Ottawa ON K1Y 4H7 Canada
加拿大K1Y 4H7渥太华C站3511号邮政信箱Dan Williston Nortel（北方电信）有限公司
EMail: danwil@Nortel.ca
EMail: danwil@Nortel.ca
Stephen Gabe Nortel (Northern Telecom), Ltd. PO Box 3511 Station C Ottawa ON K1Y 4H7 Canada
Stephen Gabe Nortel（北方电信）有限公司加拿大K1Y 4H7渥太华C站3511号邮政信箱
EMail: spgabe@Nortel.ca
EMail: spgabe@Nortel.ca
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