Internet Engineering Task Force (IETF) S. Kini, Ed.
Request for Comments: 6138 W. Lu, Ed.
Updates: 5443 Ericsson
Category: Informational February 2011
ISSN: 2070-1721
Internet Engineering Task Force (IETF) S. Kini, Ed.
Request for Comments: 6138 W. Lu, Ed.
Updates: 5443 Ericsson
Category: Informational February 2011
ISSN: 2070-1721
LDP IGP Synchronization for Broadcast Networks
广播网络中的LDP-IGP同步
Abstract
摘要
RFC 5443 describes a mechanism to achieve LDP IGP synchronization to prevent black-holing traffic (e.g., VPN) when an Interior Gateway Protocol (IGP) is operational on a link but Label Distribution Protocol (LDP) is not. If this mechanism is applied to broadcast links that have more than one LDP peer, the metric increase procedure can only be applied to the link as a whole but not to an individual peer. When a new LDP peer comes up on a broadcast network, this can result in loss of traffic through other established peers on that network. This document describes a mechanism to address that use-case without dropping traffic. The mechanism does not introduce any protocol message changes.
RFC 5443描述了当内部网关协议（IGP）在链路上可操作但标签分发协议（LDP）不可操作时，实现LDP IGP同步以防止黑洞通信（例如VPN）的机制。如果此机制应用于具有多个LDP对等点的广播链路，则度量增加过程只能应用于整个链路，而不能应用于单个对等点。当广播网络上出现新的LDP对等点时，这可能导致通过该网络上其他已建立对等点的通信量丢失。本文档描述了一种在不中断通信的情况下解决该用例的机制。该机制不会引入任何协议消息更改。
Status of This Memo
关于下段备忘
This document is not an Internet Standards Track specification; it is published for informational purposes.
本文件不是互联网标准跟踪规范；它是为了提供信息而发布的。
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/rfc6138.
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/rfc6138.
Copyright Notice
版权公告
Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2011 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
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。请审阅这些文件
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.
请仔细阅读，因为他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 ....................................................2
2. Conventions Used in This Document ...............................2
3. Problem Statement ...............................................2
4. Solution ........................................................4
5. Scope ...........................................................5
6. Applicability ...................................................5
7. Security Considerations .........................................6
8. Conclusions .....................................................6
9. References ......................................................7
9.1. Normative References .......................................7
9.2. Informative References .....................................7
Acknowledgments ....................................................7
Appendix A. Computation of "Cut-Edge" ..............................8
Appendix B. Sync without Support at One End ........................8
1. Introduction ....................................................2
2. Conventions Used in This Document ...............................2
3. Problem Statement ...............................................2
4. Solution ........................................................4
5. Scope ...........................................................5
6. Applicability ...................................................5
7. Security Considerations .........................................6
8. Conclusions .....................................................6
9. References ......................................................7
9.1. Normative References .......................................7
9.2. Informative References .....................................7
Acknowledgments ....................................................7
Appendix A. Computation of "Cut-Edge" ..............................8
Appendix B. Sync without Support at One End ........................8
In RFC 5443 [LDP-IGP-SYNC], when [LDP] is not fully operational on a link, the IGP advertises the link with maximum cost to avoid any transit traffic on the link if possible. When LDP becomes operational, i.e., all the label bindings have been exchanged, the link is advertised with its correct cost. This tries to ensure that the LDP Label Switch Path (LSP) is available all along the IGP shortest path. The mechanisms in [LDP-IGP-SYNC] have limitations when applied to a broadcast link. These are described in Section 3. A solution is defined in Section 4.
在RFC 5443[LDP-IGP-SYNC]中，当[LDP]在链路上未完全运行时，IGP以最大成本播发链路，以尽可能避免链路上的任何传输流量。当LDP开始运行时，即所有标签绑定都已交换，链路将以正确的成本进行广告。这试图确保LDP标签交换路径（LSP）在IGP最短路径上始终可用。[LDP-IGP-SYNC]中的机制在应用于广播链路时具有局限性。这些在第3节中描述。第4节定义了解决方案。
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
本文件中的关键词“必须”、“不得”、“必需”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照[RFC2119]中所述进行解释。
On broadcast networks, a router's Link State Advertisement (LSA) contains a single cost to the broadcast network rather than a separate cost to each peer on the broadcast network. The operation of the mechanism in [LDP-IGP-SYNC] is analyzed using the sample topology in Figure 1, where routers A, B, C, and E are attached to a
在广播网络上，路由器的链路状态公告（LSA）包含广播网络的单个成本，而不是广播网络上每个对等方的单独成本。使用图1中的示例拓扑分析[LDP-IGP-SYNC]中机制的操作，其中路由器A、B、C和E连接到路由器A
common broadcast network. Say all links in that topology have a cost of 1 except the link A-PE3, which has a cost of 10. The use-case when router B's link to the broadcast network comes up is analyzed. Before that link comes up, traffic between PE1 and PE2 flows along the bi-directional path PE1-A-C-D-PE2, and traffic between PE1 and PE3 flows along the bi-directional path PE1-A-E-PE3.
公共广播网络。假设该拓扑中的所有链路的成本为1，但链路a-PE3的成本为10。分析了路由器B连接到广播网络的用例。在该链路接通之前，PE1和PE2之间的流量沿双向路径PE1-A-C-D-PE2流动，PE1和PE3之间的流量沿双向路径PE1-A-E-PE3流动。
| +---+ +---+
|----| B |-----------|PE2|
| +---+ +---+
+---+ +---+ | |
|PE1|----| A |----| |
+---+ +---+ | |
| | +---+ +---+ |
| |----| C |----| D |----+
| | +---+ +---+
| |
| |
| |
| | +---+
| |----| E |-------------+
| | +---+ |
| | |
| |
| +---+
+---------------------------|PE3|
+---+
| +---+ +---+
|----| B |-----------|PE2|
| +---+ +---+
+---+ +---+ | |
|PE1|----| A |----| |
+---+ +---+ | |
| | +---+ +---+ |
| |----| C |----| D |----+
| | +---+ +---+
| |
| |
| |
| | +---+
| |----| E |-------------+
| | +---+ |
| | |
| |
| +---+
+---------------------------|PE3|
+---+
Figure 1: LDP IGP Sync on a Broadcast Network
图1：广播网络上的LDP IGP同步
In one interpretation of the applicability of [LDP-IGP-SYNC] to broadcast networks, when a new router is discovered on a broadcast network, that network should avoid transit traffic until LDP becomes operational between all routers on that network. This can be achieved by having all the attached routers advertise maximum cost to that network. This should result in traffic that is being sent via that broadcast network to be diverted. However, traffic might be inadvertently diverted to the link that just came up. Until LDP becomes operational, that traffic will be black-holed. An additional problem is route churn in the entire network that results in traffic that should be unaffected taking sub-optimal paths until the high-cost metric is reverted to the normal cost. In Figure 1, when B's link to the broadcast network comes up and it is discovered by routers A, C and E, then A, B, C, and E can all start advertising maximum cost to the broadcast network. A will have B as next-hop to PE2 and will not have a LDP LSP to PE2, resulting in VPN traffic from PE1 to PE2 to be black-holed at A. The route churn at A also results in traffic between PE1 and PE3 to be unnecessarily diverted to the
在对[LDP-IGP-SYNC]适用于广播网络的一种解释中，当在广播网络上发现新路由器时，该网络应避免传输流量，直到LDP在该网络上的所有路由器之间运行。这可以通过让所有连接的路由器向该网络公布最大成本来实现。这将导致通过该广播网络发送的流量被分流。但是，流量可能会在不经意间转移到刚刚出现的链接。在自民党开始运作之前，这种通信将被封锁。另一个问题是整个网络中的路由搅动，这会导致流量不受影响，而是采用次优路径，直到高成本指标恢复为正常成本。在图1中，当B到广播网络的链接出现并且被路由器A、C和E发现时，A、B、C和E都可以开始向广播网络宣传最大成本。A将B作为到PE2的下一个跃点，并且不会有到PE2的LDP LSP，从而导致从PE1到PE2的VPN流量在A处被黑洞。A处的路由搅动也会导致PE1和PE3之间的流量被不必要地转移到
sub-optimal path PE1-A-PE3 until the maximum-cost advertisement is reverted to the normal cost.
次优路径PE1-A-PE3，直到最大成本广告恢复为正常成本。
This interpretation has the additional complexity of requiring the maximum-cost advertisement to be reverted by all routers after LDP peering between all the routers on the broadcast network is operational. This is non-trivial and needs coordination between all the routers.
这种解释具有额外的复杂性，即在广播网络上的所有路由器之间的LDP对等操作开始后，要求所有路由器恢复最大成本广告。这是非常重要的，需要所有路由器之间的协调。
In another alternative interpretation of the applicability of [LDP-IGP-SYNC] to broadcast networks, only the router whose link to the broadcast network comes up advertises maximum cost for that link, but other routers continue to advertise the normal cost. In Figure 1, when B's link to the broadcast network comes up, it advertises a high cost to the broadcast network. After the IGP has converged but the LDP peering A-B is not yet operational, A will have B as the next-hop for PE2 and will not have a LDP LSP to PE2. Since A's cost to reach B is not high, A-B-PE2 becomes the shortest path. VPN traffic from PE1 to PE2 will be dropped at A.
在[LDP-IGP-SYNC]对广播网络适用性的另一种替代解释中，只有其到广播网络的链路出现的路由器宣传该链路的最大成本，但其他路由器继续宣传正常成本。在图1中，当B连接到广播网络时，它会向广播网络宣传高成本。在IGP已收敛但LDP对等A-B尚未运行后，A将B作为PE2的下一跳，并且将不具有LDP LSP到PE2。由于A到达B的成本不高，A-B-PE2成为最短路径。从PE1到PE2的VPN流量将在A处丢弃。
The problem described above exists because the Link State Database (LSDB) of the IGP does not describe a link coming up on a broadcast network with a high bi-directional cost to all other routers on that broadcast network. A broadcast network is advertised as a pseudonode containing a list of routers to which the broadcast network is connected, and the cost of all these links from the pseudonode to each router is zero when computing SPF (Shortest Path First).
存在上述问题是因为IGP的链路状态数据库（LSDB）不描述广播网络上出现的链路，该链路对该广播网络上的所有其他路由器具有高双向成本。广播网络被广告为包含广播网络所连接的路由器列表的伪节点，并且当计算SPF（最短路径优先）时，从伪节点到每个路由器的所有这些链路的成本为零。
The solution proposed below removes the link that is coming up from the LSDB unless absolutely necessary. Only the router whose link is coming up plays a role in ensuring this. The other routers on the broadcast network are not involved. The following text describes this in more detail.
除非绝对必要，否则下面提出的解决方案会删除LSDB中的链接。只有链路即将接通的路由器才能确保这一点。广播网络上的其他路由器不涉及。下文对此进行了更详细的描述。
During the intra-area SPF algorithm execution, an additional computation is made to detect an alternate path to a directly connected network that does not have any IGP adjacencies.
在区域内SPF算法执行期间，进行额外的计算以检测到到不具有任何IGP邻接的直接连接网络的备用路径。
If a router has a directly connected network that does not have an alternate path to reach it, then the interface to that network is a "cut-edge" in the topology for that router. When a "cut-edge" goes down, the network is partitioned into two disjoint sub-graphs. This property of whether or not an interface is a "cut-edge" is used when an IGP adjacency comes up on that interface. The method to determine whether an interface is a "cut-edge" is described in Appendix A.
如果一个路由器有一个直接连接的网络，而该网络没有其他路径可以到达它，那么该网络的接口就是该路由器拓扑中的“切割边缘”。当“切边”下降时，网络被划分为两个不相交的子图。当接口上出现IGP邻接时，将使用该接口是否为“切割边”的属性。附录a中描述了确定界面是否为“切割边缘”的方法。
During IGP procedures, when the router's first adjacency to the broadcast network is coming up and the LSA is about to be updated with a link to the pseudonode of the broadcast interface, a check is made whether that interface is a "cut-edge". If it is not a "cut-edge", then the updating of the LSA with that link to the pseudonode is postponed until LDP is operational with all the LDP peers on that broadcast interface. After LDP is operational, the LSA is updated with that link to the pseudonode (and the LSA is flooded). If the interface is a "cut-edge", then the updating of the LSA MUST NOT be delayed by LDP's operational state. Note that the IGP and LDP adjacency bring-up procedures are unchanged. The conditional check of whether the interface is a "cut-edge" must be done just before the adjacency is about to be reflected in the LSA.
在IGP过程中，当路由器与广播网络的第一个邻接即将出现并且LSA即将用到广播接口的伪节点的链路来更新时，检查该接口是否是“切边”。如果它不是“切边”，则使用该链路到伪节点的LSA的更新被推迟，直到LDP与该广播接口上的所有LDP对等方一起操作为止。LDP运行后，LSA使用到伪节点的链路进行更新（LSA被淹没）。如果接口为“切割边缘”，则LSA的更新不得因LDP的运行状态而延迟。请注意，IGP和LDP邻接启动程序保持不变。必须在邻接关系即将反映在LSA中之前，对接口是否为“切割边”进行条件检查。
If the IGP is [OSPF], the Router-LSA is not updated with a "Link Type 2" (link to transit network) for that subnet until LDP is operational with all neighboring routers on that subnet.
如果IGP为[OSPF]，则在LDP与该子网上的所有相邻路由器一起运行之前，不会使用该子网上的“链路类型2”（到传输网络的链路）更新路由器LSA。
Similarly, if the IGP is [IS-IS], the "Link State PDU" is updated with an "IS Reachability TLV" (or an "Extended IS Reachability TLV") to the pseudonode after LDP is operational with all neighboring routers on that subnet.
类似地，如果IGP是[is-is]，则在LDP与该子网上的所有相邻路由器一起操作之后，“链路状态PDU”被更新为伪节点的“is可达性TLV”（或“扩展is可达性TLV”）。
Note that this solution can be introduced in a gradual manner in a network without any backward compatibility issues.
请注意，此解决方案可以在网络中逐步引入，而不会出现任何向后兼容性问题。
This document is agnostic to the method that detects LDP to be operational with a neighbor. It does not define any new method to detect that LDP is operational. At the time of publishing this document, LDP End-of-LIB [LDP-EOL] seems to be the preferred method.
本文档不知道检测LDP是否与邻居一起工作的方法。它没有定义任何新的方法来检测LDP是否可用。在发布本文件时，LDP-End of LIB[LDP-EOL]似乎是首选方法。
Issues arising out of LDP not being configured on some routers or on some interfaces are not specific to the method described in this document and are considered outside the scope of this solution.
由于某些路由器或某些接口上未配置LDP而产生的问题并非本文件中所述方法所特有，因此不在本解决方案的范围内。
The method described in this document can be easily extended to point-to-point (P2P) links. However, an implementation may continue to apply the method described in [LDP-IGP-SYNC] to P2P links but apply the method described in this document to broadcast networks. Both methods can coexist in a network.
本文档中描述的方法可以很容易地扩展到点对点（P2P）链路。然而，实现可以继续将[LDP-IGP-SYNC]中描述的方法应用于P2P链路，但将本文档中描述的方法应用于广播网络。这两种方法可以在网络中共存。
The techniques used in this document's solution enable LDP IGP synchronization in many scenarios where one end of the IGP adjacency does not support any LDP IGP sync method. This is an optional benefit and is for further study. Some ways to apply this technique to achieve that benefit are discussed in Appendix B.
本文档解决方案中使用的技术可在IGP邻接的一端不支持任何LDP IGP同步方法的许多情况下实现LDP IGP同步。这是一个可选的好处，有待进一步研究。附录B中讨论了应用该技术实现该效益的一些方法。
This document does not introduce any new security considerations beyond those already described in [LDP-IGP-SYNC].
除[LDP-IGP-SYNC]中已经描述的安全注意事项外，本文件不引入任何新的安全注意事项。
Note that in [LDP-IGP-SYNC], when a link is advertised with a high metric, an alternate path with a large number of hops can result in the end-to-end path having more than 255 hops and thus result in unreachability. This fact could be exploited if control of metrics falls into the hands of an attacker.
注意，在[LDP-IGP-SYNC]中，当链路以高度量播发时，具有大量跳数的备用路径可导致端到端路径具有超过255跳数，从而导致不可到达性。如果度量的控制权落入攻击者手中，则可以利用这一事实。
This problem can even exist in a plain IP network with a link-state IGP. If the directly connected path has a higher metric than an alternate path with Time to Live (TTL) greater than 255 hops, then the standard SPF algorithm will conclude that the shortest path is the alternate path although the neighboring node is unreachable through this path. In this case, the link is advertised with its normal metric yet there is unreachability in the network. Thus, this document does not introduce any new issues beyond those in a standard IGP-based IP network, and operators need to apply policy and security to the techniques used to determine and distribute the metrics used on links in their networks.
这个问题甚至可以存在于链路状态为IGP的普通IP网络中。如果直接连接的路径具有比生存时间（TTL）大于255跳的备用路径更高的度量，则标准SPF算法将得出结论，最短路径是备用路径，尽管通过该路径无法到达相邻节点。在这种情况下，链路以其正常度量进行广告，但网络中存在不可到达性。因此，除了基于标准IGP的IP网络中的问题外，本文件不会引入任何新问题，运营商需要对用于确定和分发其网络中链路上使用的指标的技术应用策略和安全性。
This document complements [LDP-IGP-SYNC] by providing a solution to achieve LDP IGP synchronization for broadcast networks. It can also coexist with that solution in a network that has a combination of P2P links and broadcast networks. It can also be introduced into a network without backward compatibility issues. The solution in this document can also be used exclusively to achieve LDP IGP synchronization since this solution applies to both P2P links and broadcast networks.
本文件补充了[LDP-IGP-SYNC]，提供了实现广播网络LDP-IGP同步的解决方案。它还可以在一个结合了P2P链接和广播网络的网络中与该解决方案共存。也可以将其引入网络，而不存在向后兼容性问题。本文档中的解决方案也可专门用于实现LDP IGP同步，因为该解决方案同时适用于P2P链路和广播网络。
This solution also has useful properties that can be optionally used to achieve LDP IGP synchronization when only one end of the IGP adjacency supports this solution but the other end supports neither this solution nor the one in [LDP-IGP-SYNC].
该解决方案还具有有用的特性，当只有IGP邻接的一端支持该解决方案，但另一端既不支持该解决方案，也不支持[LDP-IGP-SYNC]中的解决方案时，可以选择使用该特性来实现LDP-IGP同步。
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2119]Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
[LDP-IGP-SYNC] Jork, M., Atlas, A., and L. Fang, "LDP IGP Synchronization", RFC 5443, March 2009.
[LDP-IGP-SYNC]Jork，M.，Atlas，A.，和L.Fang，“LDP-IGP同步”，RFC 54432009年3月。
[LDP] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed., "LDP Specification", RFC 5036, October 2007.
[LDP]Andersson，L.，Ed.，Minei，I.，Ed.，和B.Thomas，Ed.，“LDP规范”，RFC 5036，2007年10月。
[OSPF] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[OSPF]Moy，J.，“OSPF版本2”，STD 54，RFC 23281998年4月。
[IS-IS] International Organization for Standardization, "Intermediate System to Intermediate System intra-domain routeing information exchange protocol for use in conjunction with the protocol for providing the connectionless-mode network service (ISO 8473)", ISO Standard 10589, 2002.
[IS-IS]国际标准化组织，“与提供无连接模式网络服务协议一起使用的中间系统到中间系统域内路由信息交换协议（ISO 8473）”，ISO标准10589，2002年。
[LDP-EOL] Asati, R., Mohapatra, P., Chen, E., and B. Thomas, "Signaling LDP Label Advertisement Completion", RFC 5919, August 2010.
[LDP-EOL]Asati，R.，Mohapatra，P.，Chen，E.，和B.Thomas，“信号LDP标签广告完成”，RFC 5919，2010年8月。
Acknowledgments
致谢
The authors would like to thank Luyuan Fang, Mikael Abrahamsson, Ben Niven-Jenkins, Bruno Decraene, Jeff Tantsura, and Acee Lindem for their review and useful comments.
作者要感谢方卢元、米凯尔·亚伯拉罕·哈姆森、本·尼文·詹金斯、布鲁诺·德雷恩、杰夫·坦特拉和亚齐·林登的评论和有用的评论。
Appendix A. Computation of "Cut-Edge"
附录A.“切割边缘”的计算
A "cut-edge" can be computed during an intra-area SPF run or by using results of the previous SPF run. If an SPF run was scheduled but is pending execution, that SPF MUST be executed immediately before any procedure checks whether an interface is a "cut-edge".
“切割边”可在区域内SPF运行期间或通过使用前一次SPF运行的结果进行计算。如果SPF运行已计划但正在挂起执行，则必须在任何过程检查接口是否为“切割边缘”之前立即执行该SPF。
An interface is considered a "cut-edge" if, during intra-area SPF (using Dijkstra's algorithm described in Section 16.1 of [OSPF]), there is no alternate path for the directly connected network. Alternately, a "cut-edge" can be detected by the last run of SPF if there is a lack of connectivity to the router-id of a directly connected peer via an alternate path. The router-id can be known during the adjacency bring-up process.
如果在区域内SPF期间（使用[OSPF]第16.1节中描述的Dijkstra算法），直接连接的网络没有备用路径，则接口被视为“切割边缘”。或者，如果通过备用路径与直接连接的对等方的路由器id缺乏连接，则最后一次运行SPF可以检测到“切割边缘”。在邻接启动过程中可以知道路由器id。
A "cut-edge" computation should not require any extra SPF runs. It should not increase the algorithmic complexity of SPF.
“切边”计算不应要求任何额外的SPF运行。它不应增加SPF的算法复杂性。
A useful property of the solution described in this document is that LDP IGP synchronization is achievable in many scenarios where one end of the IGP adjacency does not support any LDP IGP sync method.
本文档中描述的解决方案的一个有用特性是，在IGP邻接的一端不支持任何LDP IGP同步方法的许多场景中，LDP IGP同步是可以实现的。
For P2P links (or broadcast links on which the IGP operates in P2P mode) the applicability is straightforward. An IGP can establish a P2P adjacency on a P2P link or a broadcast link with the IGP in P2P mode. When a P2P adjacency comes up, the end of the adjacency that supports the solution in this document would not advertise the link to the other router in its LSA unless the edge is a "cut-edge" or until LDP becomes operational. Hence, neither of the two routers will have IGP next-hop as the other router unless the link is a "cut-edge". Consider Figure 1 modified such that the broadcast network is replaced by P2P links between each of A, B, C, and E. Say link A-B is coming up, but only A has implemented the solution in this document whereas B has implemented neither the solution in this document nor the solution in [LDP-IGP-SYNC]. Since A's LSA does not advertise a link to B until LDP is operational, B does not have A as next-hop. After LDP is operational, A advertises the link to B in its LSA. Hence, there is no traffic loss due to LDP LSP not being present.
对于P2P链路（或IGP在P2P模式下运行的广播链路），适用性很简单。IGP可以在P2P模式下与IGP在P2P链路或广播链路上建立P2P邻接。当出现P2P邻接时，支持本文档中解决方案的邻接末端不会在其LSA中公布到另一路由器的链路，除非该边缘是“切割边缘”或LDP开始工作。因此，除非链路是“切边”，否则两个路由器都不会将IGP下一跳作为另一个路由器。考虑修改图1，使得广播网络被A、B、C和E中的每个P2P链路所取代，称链路A B即将出现，但是只有A实现了本文档中的解决方案，而B既没有实现本文档中的解决方案，也没有实现[LDP-IGP同步]中的解决方案。由于A的LSA在LDP运行之前不会公布到B的链接，所以B没有A作为下一跳。LDP运行后，A在其LSA中向B播发链路。因此，不存在由于LDP LSP不存在而导致的流量损失。
For broadcast networks, the applicability is not straightforward and should be considered a topic for future study. One way is for the designated router (DR) to stop advertising the link in the pseudonode to the router whose link is coming up until LDP is operational.
对于广播网络，其适用性并不简单，应被视为未来研究的主题。一种方法是，指定路由器（DR）停止向链路即将出现的路由器发送伪节点中的链路广告，直到LDP开始工作。
Authors' Addresses
作者地址
Sriganesh Kini (editor) Ericsson 300 Holger Way San Jose, CA 95134 EMail: sriganesh.kini@ericsson.com
斯里加内什·基尼（编辑）爱立信加利福尼亚州圣何塞霍尔格大道300号95134电子邮件：斯里加内什。kini@ericsson.com
Wenhu Lu (editor) Ericsson 300 Holger Way San Jose, CA 95134 EMail: wenhu.lu@ericsson.com
卢文虎（编辑）爱立信加利福尼亚州圣何塞霍尔格大道300号95134电子邮件：文虎。lu@ericsson.com