Internet Engineering Task Force (IETF)                          A. Atlas
Request for Comments: 7823                                      J. Drake
Category: Informational                                 Juniper Networks
ISSN: 2070-1721                                             S. Giacalone
                                                              S. Previdi
                                                           Cisco Systems
                                                                May 2016
Internet Engineering Task Force (IETF)                          A. Atlas
Request for Comments: 7823                                      J. Drake
Category: Informational                                 Juniper Networks
ISSN: 2070-1721                                             S. Giacalone
                                                              S. Previdi
                                                           Cisco Systems
                                                                May 2016

Performance-Based Path Selection for Explicitly Routed Label Switched Paths (LSPs) Using TE Metric Extensions




In certain networks, it is critical to consider network performance criteria when selecting the path for an explicitly routed RSVP-TE Label Switched Path (LSP). Such performance criteria can include latency, jitter, and loss or other indications such as the conformance to link performance objectives and non-RSVP TE traffic load. This specification describes how a path computation function may use network performance data, such as is advertised via the OSPF and IS-IS TE metric extensions (defined outside the scope of this document) to perform such path selections.

在某些网络中,当选择显式路由RSVP TE标签交换路径(LSP)时,考虑网络性能标准是至关重要的。此类性能标准可包括延迟、抖动和丢失或其他指示,如符合链路性能目标和非RSVP TE流量负载。本规范描述了路径计算功能如何使用网络性能数据,例如通过OSPF和is-is TE度量扩展(定义在本文档范围之外)公布的数据来执行此类路径选择。

Status of This Memo


This document is not an Internet Standards Track specification; it is published for informational purposes.


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


Copyright Notice


Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved.

版权所有(c)2016 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 ( 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(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


   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Basic Requirements  . . . . . . . . . . . . . . . . . . .   4
     1.2.  Oscillation and Stability Considerations  . . . . . . . .   4
   2.  Using Performance Data Constraints  . . . . . . . . . . . . .   5
     2.1.  End-to-End Constraints  . . . . . . . . . . . . . . . . .   5
     2.2.  Link Constraints  . . . . . . . . . . . . . . . . . . . .   6
     2.3.  Links out of Compliance with Link Performance Objectives    6
       2.3.1.  Use of Anomalous Links for New Paths  . . . . . . . .   7
       2.3.2.  Links Entering the Anomalous State  . . . . . . . . .   7
       2.3.3.  Links Leaving the Anomalous State . . . . . . . . . .   8
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   4.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     4.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   9
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10
   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Basic Requirements  . . . . . . . . . . . . . . . . . . .   4
     1.2.  Oscillation and Stability Considerations  . . . . . . . .   4
   2.  Using Performance Data Constraints  . . . . . . . . . . . . .   5
     2.1.  End-to-End Constraints  . . . . . . . . . . . . . . . . .   5
     2.2.  Link Constraints  . . . . . . . . . . . . . . . . . . . .   6
     2.3.  Links out of Compliance with Link Performance Objectives    6
       2.3.1.  Use of Anomalous Links for New Paths  . . . . . . . .   7
       2.3.2.  Links Entering the Anomalous State  . . . . . . . . .   7
       2.3.3.  Links Leaving the Anomalous State . . . . . . . . . .   8
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   4.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     4.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   9
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10
1. Introduction
1. 介绍

In certain networks, such as financial information networks, network performance information is becoming as critical to data-path selection as other existing metrics. Network performance information can be obtained via either the TE Metric Extensions in OSPF [RFC7471] or IS-IS [RFC7810] or via a management system. As with other TE information flooded via OSPF or IS-IS, the TE metric extensions have a flooding scope limited to the local area or level. This document describes how a path computation function, whether in an ingress LSR or a PCE [RFC4655], can use that information for path selection for explicitly routed LSPs. The selected path may be signaled via RSVP-TE [RFC3209] [RFC3473] or simply used by the ingress with segment


routing [SEG-ROUTE-MPLS] to properly forward the packet. Methods of optimizing path selection for multiple parameters are generally computationally complex. However, there are good heuristics for the delay-constrained lowest-cost (DCLC) computation problem [k-Paths_DCLC] that can be applied to consider both path cost and a maximum delay bound. Some of the network performance information can also be used to prune links from a topology before computing the path.

路由[SEG-ROUTE-MPLS]以正确转发数据包。多参数路径选择的优化方法通常计算复杂。然而,对于延迟约束的最低成本(DCLC)计算问题[K-PosisS.DCLC ]有很好的启发,可以应用于考虑路径代价和最大延迟界。在计算路径之前,还可以使用一些网络性能信息来修剪拓扑中的链接。

The path selection mechanisms described in this document apply to paths that are fully computed by the head-end of the LSP and then signaled in an Explicit Route Object (ERO) where every sub-object is strict. This allows the head-end to consider IGP-distributed performance data without requiring the ability to signal the performance constraints in an object of the RSVP Path message.


When considering performance-based data, it is obvious that there are additional contributors to latency beyond just the links. Clearly end-to-end latency is a combination of router latency (e.g., latency from traversing a router without queueing delay), queuing latency, physical link latency, and other factors. While traversing a router can cause delay, that router latency can be included in the advertised link delay. As described in [RFC7471] and [RFC7810], queuing delay must not be included in the measurements advertised by OSPF or IS-IS.


Queuing latency is specifically excluded to insure freedom from oscillations and stability issues that have plagued prior attempts to use delay as a routing metric. If application traffic follows a path based upon latency constraints, the same traffic might be in an Expedited Forwarding Per-Hop Behavior (PHB) [RFC3246] with minimal queuing delay or another PHB with potentially very substantial per-hop queuing delay. Only traffic that experiences relatively low congestion, such as Expedited Forwarding traffic, will experience delays very close to the sum of the reported link delays.


This document does not specify how a router determines what values to advertise by the IGP; it does assume that the constraints specified in [RFC7471] and [RFC7810] are followed. Additionally, the end-to-end performance that is computed for an LSP path should be built from the individual link data. Any end-to-end characterization used to determine an LSP's performance compliance should be fully reflected in the Traffic Engineering Database so that a path calculation can also determine whether a path under consideration would be in compliance.


1.1. Basic Requirements
1.1. 基本要求

The following are the requirements considered for a path computation function that uses network performance criteria.


1. Select a TE tunnel's path based upon a combination of existing constraints as well as on link-latency, packet loss, jitter, conformance with link performance objectives, and bandwidth consumed by non-RSVP-TE traffic.

1. 基于现有约束的组合以及链路延迟、数据包丢失、抖动、与链路性能目标的一致性以及非RSVP TE流量消耗的带宽,选择TE隧道的路径。

2. Ability to define different end-to-end performance requirements for each TE tunnel regardless of common use of resources.

2. 能够为每个TE隧道定义不同的端到端性能要求,而不考虑资源的共同使用。

3. Ability to periodically verify with the TE Link State Database (LSDB) that a TE tunnel's current LSP complies with its configured end-to-end performance requirements.

3. 能够使用TE链路状态数据库(LSDB)定期验证TE隧道的当前LSP是否符合其配置的端到端性能要求。

4. Ability to move tunnels, using make-before-break, based upon computed end-to-end performance complying with constraints.

4. 基于符合约束条件的计算端到端性能,使用先通后断的方式移动隧道的能力。

5. Ability to move tunnels away from any link that is violating an underlying link performance objective.

5. 能够将隧道从任何违反基本链路性能目标的链路移开。

6. Ability to optionally avoid setting up tunnels using any link that is violating a link performance objective, regardless of whether end-to-end performance would still meet requirements.

6. 能够选择性地避免使用任何违反链路性能目标的链路建立隧道,而不管端到端性能是否仍然满足要求。

7. Ability to revert back, using make-before-break, to the best path after a configurable period.

7. 能够使用先通后断,在可配置的时间段后恢复到最佳路径。

1.2. Oscillation and Stability Considerations
1.2. 振荡和稳定性考虑

Past attempts to use unbounded delay or loss as a metric suffered from severe oscillations. The use of performance based data must be such that undamped oscillations are not possible and stability cannot be impacted.


The use of timers is often cited as a cure. Oscillation that is damped by timers is known as "slosh". If advertisement timers are very short relative to the jitter applied to RSVP-TE Constrained Shortest Path First (CSPF) timers, then a partial oscillation occurs. If RSVP-TE CSPF timers are short relative to advertisement timers, full oscillation (all traffic moving back and forth) can occur. Even a partial oscillation causes unnecessary reordering that is considered at least minimally disruptive.

使用计时器经常被认为是一种治疗方法。由定时器阻尼的振荡称为“晃动”。如果广告定时器相对于应用于RSVP-TE约束最短路径优先(CSPF)定时器的抖动非常短,则会发生部分振荡。如果RSVP-TE CSPF定时器相对于广告定时器较短,则可能发生完全振荡(所有通信量来回移动)。即使是部分振荡也会导致不必要的重新排序,这至少被认为是破坏性最小的。

Delay variation or jitter is affected by even small traffic levels. At even tiny traffic levels, the probability of a queue occupancy of one can produce a measured jitter proportional to or equal to the packet serialization delay. Very low levels of traffic can increase the probability of queue occupancies of two or three packets enough to further increase the measured jitter. Because jitter measurement is extremely sensitive to very low traffic levels, any use of jitter is likely to oscillate. However, there may be uses of a jitter measurement in path computation that can be considered free of oscillation.


Delay measurements that are not sensitive to traffic loads may be safely used in path computation. Delay measurements made at the link layer or measurements made at a queuing priority higher than any significant traffic (such as Differentiated Services Code Point (DSCP) CS7 or CS6 [RFC4594], but not CS2 if traffic levels at CS3 and higher or Expedited Forwarding and Assured Forwarding can affect the measurement). Making delay measurements at the same priority as the traffic on affected paths is likely to cause oscillations.


2. Using Performance Data Constraints
2. 使用性能数据约束
2.1. End-to-End Constraints
2.1. 端到端约束

The per-link performance data available in the IGP [RFC7471] [RFC7810] includes: unidirectional link delay, unidirectional delay variation, and link loss. Each (or all) of these parameters can be used to create the path-level link-based parameter.


It is possible to compute a CSPF where the link latency values are used instead of TE metrics; this results in ignoring the TE metrics and causing LSPs to prefer the lowest-latency paths. In practical scenarios, latency constraints are typically a bound constraint rather than a minimization objective. An end-to-end latency upper bound merely requires that the path computed be no more than that bound and does not require that it be the minimum latency path. The latter is exactly the DCLC problem to which good heuristics have been proposed in the literature (e.g., [k-Paths_DCLC]).


An end-to-end bound on delay variation can be used similarly as a constraint in the path computation on what links to explore where the path's delay variation is the sum of the used links' delay variations.


   For link loss, the path loss is not the sum of the used links'
   losses.  Instead, the path loss fraction is 1 - (1 - loss_L1)*
   (1 - loss_L2)*...*(1 - loss_Ln), where the links along the path are
   L1 to Ln with loss_Li in fractions.  This computation is discussed in
   For link loss, the path loss is not the sum of the used links'
   losses.  Instead, the path loss fraction is 1 - (1 - loss_L1)*
   (1 - loss_L2)*...*(1 - loss_Ln), where the links along the path are
   L1 to Ln with loss_Li in fractions.  This computation is discussed in

more detail in Sections 5.1.4 and 5.1.5 in [RFC6049]. The end-to-end link loss bound, computed in this fashion, can also be used as a constraint in the path computation.


The heuristic algorithms for DCLC only address one constraint bound but having a CSPF that limits the paths explored (i.e., based on hop count) can be combined [hop-count_DCLC].


2.2. Link Constraints
2.2. 链接约束

In addition to selecting paths that conform to a bound on performance data, it is also useful to avoid using links that do not meet a necessary constraint. Naturally, if such a parameter were a known fixed value, then resource attribute flags could be used to express this behavior. However, when the parameter associated with a link may vary dynamically, there is not currently a configuration-time mechanism to enforce such behavior. An example of this is described in Section 2.3, where links may move in and out of conformance for link performance objectives with regards to latency, delay variation, and link loss.


When doing path selection for TE tunnels, it has not been possible to know how much actual bandwidth is available that includes the bandwidth used by non-RSVP-TE traffic. In [RFC7471] and [RFC7810], the Unidirectional Available Bandwidth is advertised as is the Residual Bandwidth. When computing the path for a TE tunnel, only links with at least a minimum amount of Unidirectional Available Bandwidth might be permitted.

在为TE隧道进行路径选择时,不可能知道有多少实际带宽可用,其中包括非RSVP TE流量使用的带宽。在[RFC7471]和[RFC7810]中,单向可用带宽与剩余带宽一样公布。当计算TE隧道的路径时,可能只允许具有至少最小单向可用带宽的链路。

Similarly, only links whose loss is under a configurable value might be acceptable. For these constraints, each link can be tested against the constraint and only explored in the path computation if the link passes. In essence, a link that fails the constraint test is treated as if it contained a resource attribute in the exclude-any filter.


2.3. Links out of Compliance with Link Performance Objectives
2.3. 链接不符合链接性能目标

Link conformance to a link performance objective can change as a result of rerouting at lower layers. This could be due to optical regrooming or simply rerouting of an FA-LSP. When this occurs, there are two questions to be asked:


a. Should the link be trusted and used for the setup of new LSPs?

a. 是否应信任该链接并将其用于设置新的LSP?

b. Should LSPs using this link automatically be moved to a secondary path?

b. 使用此链接的LSP是否应自动移动到辅助路径?

2.3.1. Use of Anomalous Links for New Paths
2.3.1. 为新路径使用异常链接

If the answer to (a) is no for link latency performance objectives, then any link that has the Anomalous bit set in the Unidirectional Link Delay sub-TLV [RFC7471] [RFC7810] should be removed from the topology before a path calculation is used to compute a new path. In essence, the link should be treated exactly as if it fails the exclude-any resource attributes filter [RFC3209].


Similarly, if the answer to (a) is no for link loss performance objectives, then any link that has the Anomalous bit set in the Link Loss sub-TLV should be treated as if it fails the exclude-any resource attributes filter.


2.3.2. Links Entering the Anomalous State
2.3.2. 链接进入异常状态

When the Anomalous bit transitions from clear to set, this indicates that the associated link has entered the Anomalous state with respect to the associated parameter; similarly, a transition from set to clear indicates that the Anomalous state has been exited for that link and associated parameter.


When a link enters the Anomalous state with respect to a parameter, this is an indication that LSPs using that link might also no longer be in compliance with their performance bounds. It can also be considered an indication that something is changing that link and so it might no longer be trustworthy to carry performance-critical traffic. Naturally, which performance criteria are important for a particular LSP is dependent upon the LSP's configuration; thus, the compliance of a link with respect to a particular link performance objective is indicated per performance criterion.


At the ingress of a TE tunnel, a TE tunnel may be configured to be sensitive to the Anomalous state of links in reference to latency, delay variation, and/or loss. Additionally, such a TE tunnel may be configured to either verify continued compliance, to switch immediately to a standby LSP, or to move to a different path.


When a sub-TLV is received with the Anomalous bit set when previously it was clear, the list of interested TE tunnels must be scanned. Each such TE tunnel should have its continued compliance verified, be switched to a hot standby, or do a make-before-break to a secondary path.


It is not sufficient to just look at the Anomalous bit in order to determine when TE tunnels must have their compliance verified. When changing to set, the Anomalous bit merely provides a hint that


interested TE tunnels should have their continued compliance verified.


2.3.3. Links Leaving the Anomalous State
2.3.3. 脱离异常状态的链接

When a link leaves the Anomalous state with respect to a parameter, this can serve as an indication that those TE tunnels, whose LSPs were changed due to administrative policy when the link entered the Anomalous state, may want to reoptimize to a better path. The hint provided by the Anomalous state change may help optimize when to recompute for a better path.


3. Security Considerations
3. 安全考虑

This document is not currently believed to introduce new security concerns.


4. References
4. 工具书类
4.1. Normative References
4.1. 规范性引用文件

[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, <>.

[RFC3209]Awduche,D.,Berger,L.,Gan,D.,Li,T.,Srinivasan,V.,和G.Swallow,“RSVP-TE:LSP隧道RSVP的扩展”,RFC 3209,DOI 10.17487/RFC3209,2001年12月<>.

[RFC7471] Giacalone, S., Ward, D., Drake, J., Atlas, A., and S. Previdi, "OSPF Traffic Engineering (TE) Metric Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015, <>.

[RFC7471]Giacalone,S.,Ward,D.,Drake,J.,Atlas,A.,和S.Previdi,“OSPF交通工程(TE)度量扩展”,RFC 7471,DOI 10.17487/RFC7471,2015年3月<>.

[RFC7810] Previdi, S., Ed., Giacalone, S., Ward, D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE) Metric Extensions", RFC 7810, DOI 10.17487/7810, May 2016, <>.

[RFC7810]Previdi,S.,Ed.,Giacalone,S.,Ward,D.,Drake,J.,和Q.Wu,“IS-IS交通工程(TE)度量扩展”,RFC 7810,DOI 10.17487/7810,2016年5月<>.

4.2. Informative References
4.2. 资料性引用

[hop-count_DCLC] Agrawal, H., Grah, M., and M. Gregory, "Optimization of QoS Routing", 6th IEEE/AACIS International Conference on Computer and Information Science, DOI 10.1109/ICIS.2007.144, July 2007, < articleDetails.jsp?arnumber=4276447>.

[hop-count_DCLC]Agrawal,H.,Grah,M.和M.Gregory,“QoS路由优化”,第六届IEEE/AACIS计算机和信息科学国际会议,DOI 10.1109/ICIS.2007.144,2007年7月< articleDetails.jsp?arnumber=4276447>。

[k-Paths_DCLC] Jia, Z. and P. Varaiya, "Heuristic methods for delay constrained least cost routing using k-shortest-paths", IEEE Transactions on Automatic Control, vol. 51, no. 4, April 2006, <>.


[RFC3246] Davie, B., Charny, A., Bennet, J., Benson, K., Le Boudec, J., Courtney, W., Davari, S., Firoiu, V., and D. Stiliadis, "An Expedited Forwarding PHB (Per-Hop Behavior)", RFC 3246, DOI 10.17487/RFC3246, March 2002, <>.

[RFC3246]Davie,B.,Charny,A.,Bennet,J.,Benson,K.,Le Boudec,J.,Courtney,W.,Davari,S.,Firoiu,V.,和D.Stiliadis,“快速转发PHB(每跳行为)”,RFC 3246,DOI 10.17487/RFC3246,2002年3月<>.

[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC 3473, DOI 10.17487/RFC3473, January 2003, <>.

[RFC3473]Berger,L.,Ed.“通用多协议标签交换(GMPLS)信令资源预留协议流量工程(RSVP-TE)扩展”,RFC 3473,DOI 10.17487/RFC3473,2003年1月<>.

[RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration Guidelines for DiffServ Service Classes", RFC 4594, DOI 10.17487/RFC4594, August 2006, <>.

[RFC4594]Babiarz,J.,Chan,K.,和F.Baker,“区分服务服务类的配置指南”,RFC 4594,DOI 10.17487/RFC4594,2006年8月<>.

[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, DOI 10.17487/RFC4655, August 2006, <>.

[RFC4655]Farrel,A.,Vasseur,J.,和J.Ash,“基于路径计算元素(PCE)的体系结构”,RFC 4655,DOI 10.17487/RFC4655,2006年8月<>.

[RFC6049] Morton, A. and E. Stephan, "Spatial Composition of Metrics", RFC 6049, DOI 10.17487/RFC6049, January 2011, <>.

[RFC6049]Morton,A.和E.Stephan,“度量的空间构成”,RFC 6049,DOI 10.17487/RFC6049,2011年1月<>.

[SEG-ROUTE-MPLS] Filsfils, C., Ed., Previdi, S., Ed., Bashandy, A., Decraene, B., Litkowski, S., Horneffer, M., Shakir, R., Tantsura, J., and E. Crabbe, "Segment Routing with MPLS data plane", Work in Progress, draft-ietf-spring-segment-routing-mpls-04, March 2016.




The authors would like to thank Curtis Villamizar for his extensive detailed comments and suggested text in Sections 1 and 1.2. The authors would like to thank Dhruv Dhody for his useful comments and his care and persistence in making sure that these important corrections weren't missed. The authors would also like to thank Xiaohu Xu and Sriganesh Kini for their reviews.

作者感谢Curtis Villamizar在第1节和第1.2节中提出的广泛详细评论和建议文本。作者要感谢Dhruv Dhody的有用评论,以及他在确保这些重要更正不被遗漏方面的关心和坚持。作者还要感谢徐晓虎和斯里加内什·基尼的评论。



Dave Ward and Clarence Filsfils contributed to this document.

Dave Ward和Clarence Filsfils对此文档做出了贡献。

Authors' Addresses


Alia Atlas Juniper Networks 10 Technology Park Drive Westford, MA 01886 United States

美国马萨诸塞州韦斯特福德科技园大道10号Alia Atlas Juniper Networks 01886


John Drake Juniper Networks 1194 N. Mathilda Ave. Sunnyvale, CA 94089 United States



Spencer Giacalone Microsoft



Stefano Previdi Cisco Systems Via Del Serafico 200 Rome 00142 Italy

Stefano Previdi Cisco Systems Via Del Serafico 200意大利罗马00142