Internet Engineering Task Force (IETF) V. Fuller
Request for Comments: 6836
Category: Experimental D. Farinacci
ISSN: 2070-1721 D. Meyer
D. Lewis
Cisco Systems
January 2013
Internet Engineering Task Force (IETF) V. Fuller
Request for Comments: 6836
Category: Experimental D. Farinacci
ISSN: 2070-1721 D. Meyer
D. Lewis
Cisco Systems
January 2013
Locator/ID Separation Protocol Alternative Logical Topology (LISP+ALT)
定位器/ID分离协议替代逻辑拓扑（LISP+ALT）
Abstract
摘要
This document describes a simple distributed index system to be used by a Locator/ID Separation Protocol (LISP) Ingress Tunnel Router (ITR) or Map-Resolver (MR) to find the Egress Tunnel Router (ETR) that holds the mapping information for a particular Endpoint Identifier (EID). The MR can then query that ETR to obtain the actual mapping information, which consists of a list of Routing Locators (RLOCs) for the EID. Termed the Alternative Logical Topology (ALT), the index is built as an overlay network on the public Internet using the Border Gateway Protocol (BGP) and Generic Routing Encapsulation (GRE).
本文档描述了一个简单的分布式索引系统，用于定位器/ID分离协议（LISP）入口隧道路由器（ITR）或映射解析器（MR）查找出口隧道路由器（ETR），该路由器保存特定端点标识符（EID）的映射信息。然后，MR可以查询该ETR以获得实际映射信息，该信息包括EID的路由定位器（RLOC）列表。该索引称为替代逻辑拓扑（ALT），使用边界网关协议（BGP）和通用路由封装（GRE）在公共互联网上构建为覆盖网络。
Status of This Memo
关于下段备忘
This document is not an Internet Standards Track specification; it is published for examination, experimental implementation, and evaluation.
本文件不是互联网标准跟踪规范；它是为检查、实验实施和评估而发布的。
This document defines an Experimental Protocol for the Internet community. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741.
本文档为互联网社区定义了一个实验协议。本文件是互联网工程任务组（IETF）的产品。它代表了IETF社区的共识。它已经接受了公众审查，并已被互联网工程指导小组（IESG）批准出版。并非IESG批准的所有文件都适用于任何级别的互联网标准；见RFC 5741第2节。
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6836.
有关本文件当前状态、任何勘误表以及如何提供反馈的信息，请访问http://www.rfc-editor.org/info/rfc6836.
Copyright Notice
版权公告
Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2013 IETF信托基金和确定为文件作者的人员。版权所有。
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(http://trustee.ietf.org/license-info)自本文件出版之日起生效。请仔细阅读这些文件，因为它们描述了您对本文件的权利和限制。从本文件中提取的代码组件必须包括信托法律条款第4.e节中所述的简化BSD许可证文本，并提供简化BSD许可证中所述的无担保。
Table of Contents
目录
1. Introduction ....................................................3
2. Definition of Terms .............................................5
3. The LISP-ALT Model ..............................................8
3.1. Routability of EIDs ........................................8
3.1.1. Mechanisms for an ETR to Originate EID-Prefixes .....9
3.1.2. Mechanisms for an ITR to Forward to EID-Prefixes ....9
3.1.3. Map-Server Model Preferred ..........................9
3.2. Connectivity to Non-LISP Sites ............................10
3.3. Caveats on the Use of Data-Probes .........................10
4. LISP+ALT: Overview .............................................10
4.1. ITR Traffic Handling ......................................11
4.2. EID Assignment - Hierarchy and Topology ...................12
4.3. Use of GRE and BGP between LISP-ALT Routers ...............14
5. EID-Prefix Propagation and Map-Request Forwarding ..............14
5.1. Changes to ITR Behavior with LISP+ALT .....................15
5.2. Changes to ETR Behavior with LISP+ALT .....................15
5.3. ALT Datagram Forwarding Failure ...........................16
6. BGP Configuration and Protocol Considerations ..................16
6.1. Autonomous System Numbers (ASNs) in LISP+ALT ..............16
6.2. Subsequent Address Family Identifier (SAFI) for LISP+ALT ..17
7. EID-Prefix Aggregation .........................................17
7.1. Stability of the ALT ......................................18
7.2. Traffic Engineering Using LISP ............................18
7.3. Edge Aggregation and Dampening ............................19
7.4. EID Assignment Flexibility vs. ALT Scaling ................19
8. Connecting Sites to the ALT Network ............................20
8.1. ETRs Originating Information into the ALT .................20
8.2. ITRs Using the ALT ........................................21
9. Security Considerations ........................................22
9.1. Apparent LISP+ALT Vulnerabilities .........................22
9.2. Survey of LISP+ALT Security Mechanisms ....................23
9.3. Use of Additional BGP Security Mechanisms .................24
10. Acknowledgments ...............................................24
11. References ....................................................24
11.1. Normative References .....................................24
11.2. Informative References ...................................25
1. Introduction ....................................................3
2. Definition of Terms .............................................5
3. The LISP-ALT Model ..............................................8
3.1. Routability of EIDs ........................................8
3.1.1. Mechanisms for an ETR to Originate EID-Prefixes .....9
3.1.2. Mechanisms for an ITR to Forward to EID-Prefixes ....9
3.1.3. Map-Server Model Preferred ..........................9
3.2. Connectivity to Non-LISP Sites ............................10
3.3. Caveats on the Use of Data-Probes .........................10
4. LISP+ALT: Overview .............................................10
4.1. ITR Traffic Handling ......................................11
4.2. EID Assignment - Hierarchy and Topology ...................12
4.3. Use of GRE and BGP between LISP-ALT Routers ...............14
5. EID-Prefix Propagation and Map-Request Forwarding ..............14
5.1. Changes to ITR Behavior with LISP+ALT .....................15
5.2. Changes to ETR Behavior with LISP+ALT .....................15
5.3. ALT Datagram Forwarding Failure ...........................16
6. BGP Configuration and Protocol Considerations ..................16
6.1. Autonomous System Numbers (ASNs) in LISP+ALT ..............16
6.2. Subsequent Address Family Identifier (SAFI) for LISP+ALT ..17
7. EID-Prefix Aggregation .........................................17
7.1. Stability of the ALT ......................................18
7.2. Traffic Engineering Using LISP ............................18
7.3. Edge Aggregation and Dampening ............................19
7.4. EID Assignment Flexibility vs. ALT Scaling ................19
8. Connecting Sites to the ALT Network ............................20
8.1. ETRs Originating Information into the ALT .................20
8.2. ITRs Using the ALT ........................................21
9. Security Considerations ........................................22
9.1. Apparent LISP+ALT Vulnerabilities .........................22
9.2. Survey of LISP+ALT Security Mechanisms ....................23
9.3. Use of Additional BGP Security Mechanisms .................24
10. Acknowledgments ...............................................24
11. References ....................................................24
11.1. Normative References .....................................24
11.2. Informative References ...................................25
This document describes the LISP+ALT system, used by an [RFC6830] Ingress Tunnel Router (ITR) or MR to find the Egress Tunnel Router (ETR) that holds the RLOC mapping information for a particular Endpoint Identifier (EID). The ALT network is built using the Border Gateway Protocol (BGP) [RFC4271], BGP multiprotocol extensions
本文档描述了LISP+ALT系统，[RFC6830]入口隧道路由器（ITR）或MR使用该系统查找出口隧道路由器（ETR），该路由器保存特定端点标识符（EID）的RLOC映射信息。ALT网络使用边界网关协议（BGP）[RFC4271]，BGP多协议扩展构建
[RFC4760], and Generic Routing Encapsulation (GRE) [RFC2784] to construct an overlay network of devices (ALT-Routers) that operate on EID-Prefixes and use EIDs as forwarding destinations.
[RFC4760]和通用路由封装（GRE）[RFC2784]构建一个覆盖设备网络（ALT路由器），这些设备在EID前缀上运行，并使用EID作为转发目的地。
ALT-Routers advertise hierarchically delegated segments of the EID namespace (i.e., prefixes) toward the rest of the ALT; they also forward traffic destined for an EID covered by one of those prefixes toward the network element that is authoritative for that EID and is the origin of the BGP advertisement for that EID-Prefix. An ITR uses this overlay to send a LISP Map-Request (defined in [RFC6830]) to the ETR that holds the EID-to-RLOC mapping for a matching EID-Prefix. In most cases, an ITR does not connect directly to the overlay network but instead sends Map-Requests via a Map-Resolver (described in [RFC6833]) that does. Likewise, in most cases, an ETR does not connect directly to the overlay network but instead registers its EID-Prefixes with a Map-Server that advertises those EID-Prefixes on to the ALT and forwards Map-Requests for them to the ETR.
ALT路由器向ALT的其余部分发布EID名称空间（即前缀）的分层委托段；它们还将发送到由这些前缀之一覆盖的EID的流量转发到对该EID具有权威性并且是该EID前缀的BGP公告来源的网元。ITR使用此覆盖向ETR发送LISP映射请求（在[RFC6830]中定义），ETR保存匹配EID前缀的EID到RLOC映射。在大多数情况下，ITR不直接连接到覆盖网络，而是通过映射解析器（如[RFC6833]中所述）发送映射请求。同样，在大多数情况下，ETR不直接连接到覆盖网络，而是向地图服务器注册其EID前缀，该服务器将这些EID前缀播发到ALT，并将其地图请求转发到ETR。
It is important to note that the ALT does not distribute actual EID-to-RLOC mappings. What it does provide is a forwarding path from an ITR (or MR) that requires an EID-to-RLOC mapping to an ETR that holds that mapping. The ITR/MR uses this path to send an ALT Datagram (see Section 3) to an ETR, which then responds with a Map-Reply containing the needed mapping information.
需要注意的是，ALT并没有将实际的EID分发到RLOC映射。它提供的是从需要EID到RLOC映射的ITR（或MR）到保存该映射的ETR的转发路径。ITR/MR使用此路径将ALT数据报（见第3节）发送到ETR，ETR随后用包含所需映射信息的映射回复进行响应。
One design goal for LISP+ALT is to use existing technology wherever possible. To this end, the ALT is intended to be built using off-the-shelf routers that already implement the required protocols (BGP and GRE); little, if any, LISP-specific modifications should be needed for such devices to be deployed on the ALT (see Section 7 for aggregation requirements). Note, though, that organizational and operational considerations suggest that ALT-Routers be both logically and physically separate from the "native" Internet packet transport system; deploying this overlay on those routers that are already participating in the global routing system and actively forwarding Internet traffic is not recommended.
LISP+ALT的一个设计目标是尽可能使用现有技术。为此，ALT计划使用已经实现所需协议（BGP和GRE）的现成路由器构建；在ALT上部署此类设备时，几乎不需要（如果有）特定于LISP的修改（聚合要求见第7节）。不过，请注意，组织和操作方面的考虑表明，ALT路由器在逻辑和物理上都与“本机”互联网数据包传输系统分离；不建议在已经参与全局路由系统并主动转发Internet流量的路由器上部署此覆盖。
This specification is experimental, and there are areas where further experience is needed to understand the best implementation strategy, operational model, and effects on Internet operations. These areas include:
本规范是实验性的，在某些领域需要进一步的经验来理解最佳实施策略、运营模式以及对互联网运营的影响。这些领域包括：
o application effects of on-demand route map discovery
o 按需路线图发现的应用效果
o tradeoff in connection setup time vs. ALT design and performance when using a Map Request instead of carrying initial user data in a Data-Probe
o 使用映射请求而不是在数据探测器中携带初始用户数据时，连接设置时间与ALT设计和性能之间的权衡
o best practical ways to build ALT hierarchies
o 构建ALT层次结构的最佳实用方法
o effects of route leakage from ALT to the current Internet, particularly for LISP-to-non-LISP interworking
o 从ALT到当前Internet的路由泄漏的影响，尤其是LISP到非LISP互通
o effects of exceptional situations, such as denial-of-service (DoS) attacks
o 异常情况的影响，例如拒绝服务（DoS）攻击
Experimentation, measurements, and deployment experience on these aspects is appreciated. While these issues are conceptually well-understood (e.g., an ALT lookup causes potential delay for the first packet destined to a given network), the real-world operational effects are much less clear.
在这些方面的实验、测量和部署经验值得赞赏。虽然这些问题在概念上已得到很好的理解（例如，ALT查找会导致发送到给定网络的第一个数据包的潜在延迟），但实际操作效果却不太清楚。
The remainder of this document is organized as follows: Section 2 provides the definitions of terms used in this document. Section 3 outlines the LISP-ALT model, where EID-Prefixes are advertised using BGP on an overlay network (the "ALT") and Map-Requests are forwarded across it. Section 4 provides a basic overview of the LISP Alternative Logical Topology architecture, and Section 5 describes how the ALT uses BGP to propagate EID reachability over the overlay network. Section 6 describes other considerations for using BGP on the ALT. Section 7 describes the construction of the ALT aggregation hierarchy, and Section 8 discusses how LISP-ALT elements are connected to form the overlay network. Section 9 discusses security considerations relevant to LISP+ALT.
本文件的其余部分组织如下：第2节提供了本文件中所用术语的定义。第3节概述了LISP-ALT模型，其中EID前缀在覆盖网络（“ALT”）上使用BGP进行广告，映射请求在覆盖网络上转发。第4节提供了LISP替代逻辑拓扑结构的基本概述，第5节描述了ALT如何使用BGP在覆盖网络上传播EID可达性。第6节描述了在ALT上使用BGP的其他注意事项。第7节描述了ALT聚合层次结构的构造，第8节讨论了如何连接LISP-ALT元素以形成覆盖网络。第9节讨论了与LISP+ALT相关的安全注意事项。
This section provides high-level definitions of LISP concepts and components involved with and affected by LISP+ALT.
本节提供与LISP+ALT相关并受其影响的LISP概念和组件的高级定义。
Alternative Logical Topology (ALT): The virtual overlay network made up of tunnels between LISP-ALT Routers. The Border Gateway Protocol (BGP) runs between ALT-Routers and is used to carry reachability information for EID-Prefixes. The ALT provides a way to forward Map-Requests (and, if supported, Data-Probes) toward the ETR that "owns" an EID-Prefix. As a tunneled overlay, its performance is expected to be quite limited, so using it to forward high-bandwidth flows of Data-Probes is strongly discouraged (see Section 3.3 for additional discussion).
替代逻辑拓扑（ALT）：由LISP-ALT路由器之间的隧道组成的虚拟覆盖网络。边界网关协议（BGP）在ALT路由器之间运行，用于传输EID前缀的可达性信息。ALT提供了一种向“拥有”EID前缀的ETR转发映射请求（以及，如果支持，数据探测）的方法。作为隧道覆盖，其性能预计将非常有限，因此强烈反对使用它转发数据探测器的高带宽流（更多讨论请参见第3.3节）。
ALT-Router: The device that runs on the ALT. The ALT is a static network built using tunnels between ALT-Routers. These routers are deployed in a roughly hierarchical mesh in which routers at each level in the topology are responsible for aggregating EID-Prefixes learned from those logically "below" them and advertising summary prefixes to those logically "above" them.
ALT路由器：在ALT上运行的设备。ALT是使用ALT路由器之间的隧道构建的静态网络。这些路由器部署在一个大致分层的网状结构中，拓扑结构中每一层的路由器负责聚合从逻辑上“低于”它们的路由器中学习到的EID前缀，并将摘要前缀发布到逻辑上“高于”它们的路由器中。
Prefix learning and propagation between ALT-Routers is done using BGP. An ALT-Router at the lowest level, or "edge" of the ALT, learns EID-Prefixes from its "client" ETRs. See Section 3.1 for a description of how EID-Prefixes are learned at the "edge" of the ALT. See also Section 6 for details on how BGP is configured between the different network elements. When an ALT-Router receives an ALT Datagram, it looks up the destination EID in its forwarding table (composed of EID-Prefix routes it learned from neighboring ALT-Routers) and forwards it to the logical next hop on the overlay network.
使用BGP完成ALT路由器之间的前缀学习和传播。最低级别的ALT路由器或ALT的“边缘”从其“客户端”ETR中学习EID前缀。有关如何在ALT的“边缘”学习EID前缀的说明，请参见第3.1节。有关如何在不同网络元素之间配置BGP的详细信息，请参见第6节。当ALT路由器接收到ALT数据报时，它在其转发表中查找目标EID（由从相邻ALT路由器学到的EID前缀路由组成），并将其转发到覆盖网络上的逻辑下一跳。
Endpoint ID (EID): A 32-bit (for IPv4) or 128-bit (for IPv6) value used to identify the ultimate source or destination for a LISP-encapsulated packet. See [RFC6830] for details.
端点ID（EID）：用于标识LISP封装数据包的最终源或目标的32位（对于IPv4）或128位（对于IPv6）值。详见[RFC6830]。
EID-Prefix: A set of EIDs delegated in a power-of-two block. Information about EID-Prefixes is exchanged among ALT-Routers (not on the global Internet) using BGP, and EID-Prefixes are expected to be assigned in a hierarchical manner such that they can be aggregated by ALT-Routers. Such a block is characterized by a prefix and a length. Note that while the ALT routing system considers an EID-Prefix to be an opaque block of EIDs, an end site may put site-local, topologically relevant structure (subnetting) into an EID-Prefix for intra-site routing.
EID前缀：在两个块的幂中委派的一组EID。关于EID前缀的信息在使用BGP的ALT路由器（不在全球互联网上）之间交换，并且EID前缀预期以分层方式分配，以便它们可以由ALT路由器聚合。这种块的特征是前缀和长度。请注意，尽管ALT路由系统将EID前缀视为EID的不透明块，但终端站点可能会将站点本地拓扑相关结构（子网）放入EID前缀中，以进行站点内路由。
Aggregated EID-Prefixes: A set of individual EID-Prefixes that have been aggregated in the [RFC4632] sense.
聚合EID前缀：在[RFC4632]意义上聚合的一组单个EID前缀。
Map-Server (MS): An edge ALT-Router that provides a registration function for non-ALT-connected ETRs, originates EID-Prefixes into the ALT on behalf of those ETRs, and forwards Map-Requests to them. See [RFC6833] for details.
地图服务器（MS）：边缘ALT路由器，为非ALT连接的ETR提供注册功能，代表这些ETR将EID前缀发送到ALT中，并将地图请求转发给它们。详见[RFC6833]。
Map-Resolver (MR): An edge ALT-Router that accepts an Encapsulated Map-Request from a non-ALT-connected ITR, decapsulates it, and forwards it on to the ALT toward the ETR that owns the requested EID-Prefix. See [RFC6833] for details.
映射解析器（MR）：一种边缘ALT路由器，它接受来自非ALT连接的ITR的封装映射请求，将其解除封装，并将其转发到ALT上，指向拥有所请求EID前缀的ETR。详见[RFC6833]。
Ingress Tunnel Router (ITR): A router that sends LISP Map-Requests or encapsulates IP datagrams with LISP headers, as defined in [RFC6830]. In this document, "ITR" refers to any device implementing ITR functionality, including a Proxy-ITR (see [RFC6832]). Under some circumstances, a LISP Map-Resolver may also originate Map-Requests (see [RFC6833]).
入口隧道路由器（ITR）：发送LISP映射请求或用LISP头封装IP数据报的路由器，如[RFC6830]中所定义。在本文档中，“ITR”指实现ITR功能的任何设备，包括代理ITR（参见[RFC6832]）。在某些情况下，LISP映射解析器也可能发起映射请求（请参见[RFC6833]）。
Egress Tunnel Router (ETR): A router that sends LISP Map-Replies in response to LISP Map-Requests and decapsulates LISP-encapsulated IP datagrams for delivery to end-systems, as defined in [RFC6830]. In this document, "ETR" refers to any device implementing ETR functionality, including a Proxy-ETR (see [RFC6832]). Under some circumstances, a LISP Map-Server may also respond to Map-Requests (see [RFC6833]).
出口隧道路由器（ETR）：根据[RFC6830]中的定义，发送LISP Map回复以响应LISP Map请求，并对LISP封装的IP数据报进行去封装以交付给终端系统的路由器。在本文件中，“ETR”指实现ETR功能的任何设备，包括代理ETR（见[RFC6832]）。在某些情况下，LISP映射服务器也可能响应映射请求（请参见[RFC6833]）。
Routing Locator (RLOC): A routable IP address for a LISP Tunnel Router (ITR or ETR). Interchangeably referred to as a "locator" in this document. An RLOC is also the output of an EID-to-RLOC mapping lookup; an EID-Prefix maps to one or more RLOCs. Typically, RLOCs are numbered from topologically aggregatable blocks that are assigned to a site at each point where it attaches to the global Internet; where the topology is defined by the connectivity of provider networks, RLOCs can be thought of as Provider-Assigned (PA) addresses. Routing for RLOCs is not carried on the ALT.
路由定位器（RLOC）：LISP隧道路由器（ITR或ETR）的可路由IP地址。在本文件中可替换地称为“定位器”。RLOC也是EID到RLOC映射查找的输出；EID前缀映射到一个或多个RLOC。通常，RLOC从拓扑上可聚合的块中进行编号，这些块在其连接到全球互联网的每个点处分配给站点；如果拓扑由提供商网络的连接性定义，则可以将RLOC视为提供商分配（PA）地址。RLOC的路由不在ALT上进行。
EID-to-RLOC Mapping: A binding between an EID-Prefix and the set of RLOCs that can be used to reach it; sometimes simply referred to as a "mapping".
EID到RLOC映射：EID前缀和可用于访问它的RLOC集之间的绑定；有时简单地称为“映射”。
EID-Prefix Reachability: An EID-Prefix is said to be "reachable" if at least one of its Locators is reachable. That is, an EID-Prefix is reachable if the ETR that is authoritative for a given EID-to-RLOC mapping is reachable.
EID前缀可访问性：如果EID前缀至少有一个定位器是可访问的，则称其为“可访问”。也就是说，如果给定EID到RLOC映射的权威ETR是可访问的，则EID前缀是可访问的。
Default Mapping: A mapping entry for EID-Prefix 0.0.0.0/0 (::/0 for IPv6). It maps to a Locator-Set used for all EIDs in the Internet. If there is a more-specific EID-Prefix in the map-cache, it overrides the Default Mapping entry. The Default Mapping entry can be learned by configuration or from a Map-Reply message.
默认映射：EID前缀0.0.0.0/0的映射项（：：/0表示IPv6）。它映射到用于Internet中所有EID的定位器集。如果地图缓存中有更具体的EID前缀，它将覆盖默认的地图条目。默认映射条目可以通过配置或映射回复消息学习。
ALT Default Route: An EID-Prefix value of 0.0.0.0/0 (or ::/0 for IPv6) that may be learned from the ALT or statically configured on an edge ALT-Router. The ALT Default Route defines a forwarding path for a packet to be sent into the ALT on a router that does not have a full ALT forwarding database.
ALT默认路由：EID前缀值为0.0.0.0/0（对于IPv6为：：/0），可以从ALT中学习，也可以在边缘ALT路由器上静态配置。ALT默认路由为要发送到没有完整ALT转发数据库的路由器上的ALT的数据包定义转发路径。
The LISP-ALT model uses the same basic query/response protocol that is documented in [RFC6830]. In particular, LISP+ALT provides two types of packets that an ITR can originate to obtain EID-to-RLOC mappings:
LISP-ALT模型使用与[RFC6830]中所述相同的基本查询/响应协议。特别是，LISP+ALT提供了两种类型的数据包，ITR可以发起这些数据包来获得EID到RLOC的映射：
Map-Request: A Map-Request message is sent into the ALT to request an EID-to-RLOC mapping. The ETR that owns the mapping will respond to the ITR with a Map-Reply message. Since the ALT only forwards on EID destinations, the destination address of the Map-Request sent on the ALT must be an EID.
映射请求：将映射请求消息发送到ALT以请求EID到RLOC的映射。拥有映射的ETR将使用映射回复消息响应ITR。由于ALT仅在EID目的地上转发，因此在ALT上发送的映射请求的目的地地址必须是EID。
Data-Probe: Alternatively, an ITR may encapsulate and send the first data packet destined for an EID with no known RLOCs into the ALT as a Data-Probe. This might be done to minimize packet loss and to probe for the mapping. As above, the authoritative ETR for the EID-Prefix will respond to the ITR with a Map-Reply message when it receives the data packet over the ALT. As a side-effect, the encapsulated data packet is delivered to the end-system at the ETR site. Note that the Data-Probe's inner IP destination address, which is an EID, is copied to the outer IP destination address so that the resulting packet can be routed over the ALT. See Section 3.3 for caveats on the usability of Data-Probes.
数据探测：或者，ITR可以将目的地为EID且没有已知RLOC的第一个数据包作为数据探测封装并发送到ALT中。这可能是为了最小化数据包丢失和探测映射。如上所述，EID前缀的权威ETR在通过ALT接收数据包时，将使用Map回复消息对ITR作出响应。作为一种副作用，封装的数据包被传送到ETR站点的终端系统。请注意，数据探测器的内部IP目标地址（EID）被复制到外部IP目标地址，以便生成的数据包可以通过ALT路由。有关数据探测器可用性的注意事项，请参见第3.3节。
The term "ALT Datagram" is shorthand for a Map-Request or Data-Probe to be sent into or forwarded on the ALT. Note that such packets use an RLOC as the outer-header source IP address and an EID as the outer-header destination IP address.
术语“ALT数据报”是发送到ALT或在ALT上转发的映射请求或数据探测的缩写。请注意，此类数据包使用RLOC作为外部报头源IP地址，使用EID作为外部报头目标IP地址。
Detailed descriptions of the LISP packet types referenced by this document may be found in [RFC6830].
本文件引用的LISP数据包类型的详细说明见[RFC6830]。
A LISP EID has the same syntax as an IP address and can be used, unaltered, as the source or destination of an IP datagram. In general, though, EIDs are not routable on the public Internet; LISP+ ALT provides a separate, virtual network, known as the LISP Alternative Logical Topology (ALT) on which a datagram using an EID as an IP destination address may be transmitted. This network is built as an overlay on the public Internet using tunnels to interconnect ALT-Routers. BGP runs over these tunnels to propagate path information needed to forward ALT Datagrams. Importantly, while the ETRs are the source(s) of the unaggregated EID-Prefixes, LISP+ALT uses existing BGP mechanisms to aggregate this information.
LISP EID与IP地址具有相同的语法，可以作为IP数据报的源或目标使用，不作更改。不过，一般来说，EID不能在公共互联网上路由；LISP+ALT提供了一个独立的虚拟网络，称为LISP替代逻辑拓扑（ALT），在该网络上可以传输使用EID作为IP目标地址的数据报。该网络构建为覆盖在公共互联网上，使用隧道互连ALT路由器。BGP通过这些隧道传播转发ALT数据报所需的路径信息。重要的是，虽然ETR是未聚合EID前缀的来源，但LISP+ALT使用现有的BGP机制来聚合此信息。
There are three ways that an ETR may originate its mappings into the ALT:
ETR可以通过三种方式将其映射到ALT：
1. By registration with a Map-Server, as documented in [RFC6833]. This is the common case and is expected to be used by the majority of ETRs.
1. 通过向地图服务器注册，如[RFC6833]中所述。这是常见的情况，预计大多数ETR都会使用。
2. Using a "static route" on the ALT. Where no Map-Server is available, an edge ALT-Router may be configured with a "static EID-Prefix route" pointing to an ETR.
2. 在ALT上使用“静态路由”。在没有地图服务器的情况下，边缘ALT路由器可以配置指向ETR的“静态EID前缀路由”。
3. Edge connection to the ALT. If a site requires fine-grained control over how its EID-Prefixes are advertised into the ALT, it may configure its ETR(s) with tunnel and BGP connections to edge ALT-Routers.
3. 到ALT的边缘连接。如果站点需要对其EID前缀在ALT中的播发方式进行细粒度控制，则可以使用到边缘ALT路由器的隧道和BGP连接配置其ETR。
There are three ways that an ITR may send ALT Datagrams:
ITR可以通过三种方式发送ALT数据报：
1. Through a Map-Resolver, as documented in [RFC6833]. This is the common case and is expected to be used by the majority of ITRs.
1. 通过映射解析器，如[RFC6833]中所述。这是常见的情况，预计大多数ITR都会使用。
2. Using a "default route". Where a Map-Resolver is not available, an ITR may be configured with a static ALT Default Route pointing to an edge ALT-Router.
2. 使用“默认路由”。在地图解析器不可用的情况下，可以使用指向边缘ALT路由器的静态ALT默认路由配置ITR。
3. Edge connection to the ALT. If a site requires fine-grained knowledge of what prefixes exist on the ALT, it may configure its ITR(s) with tunnel and BGP connections to edge ALT-Routers.
3. 到ALT的边缘连接。如果站点需要关于ALT上存在哪些前缀的细粒度知识，则可以使用到边缘ALT路由器的隧道和BGP连接配置其ITR。
The ALT-connected ITR and ETR cases are expected to be rare, as the Map-Server/Map-Resolver model is simpler for an ITR/ETR operator to use and also provides a more general service interface to not only the ALT but to other mapping databases that may be developed in the future.
预计ALT连接的ITR和ETR案例将很少见，因为地图服务器/地图解析器模型对于ITR/ETR操作员来说使用起来更简单，而且还为ALT以及将来可能开发的其他地图数据库提供了更通用的服务接口。
As stated above, EIDs used as IP addresses by LISP sites are not routable on the public Internet. This implies that, absent a mechanism for communication between LISP and non-LISP sites, connectivity between them is not possible. To resolve this problem, an "interworking" technology has been defined; see [RFC6832] for details.
如上所述，LISP站点用作IP地址的EID不能在公共Internet上路由。这意味着，由于缺少LISP和非LISP站点之间的通信机制，它们之间的连接是不可能的。为了解决这个问题，定义了“互通”技术；详见[RFC6832]。
It is worth noting that there has been a great deal of discussion and controversy about whether Data-Probes are a good idea. On the one hand, u