Calculating Interior Gateway Protocol (IGP) Routes Over Traffic Engineering Tunnels
RFC 3906
Document | Type | RFC - Informational (October 2004; No errata) | |
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Authors | Henk Smit , Naiming Shen | ||
Last updated | 2013-03-02 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 3906 (Informational) | |
Action Holders |
(None)
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Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Alex Zinin | ||
Send notices to | fenner@research.att.com, zinin@psg.com |
Network Working Group N. Shen Request for Comments: 3906 Redback Networks Category: Informational H. Smit October 2004 Calculating Interior Gateway Protocol (IGP) Routes Over Traffic Engineering Tunnels Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2004). Abstract This document describes how conventional hop-by-hop link-state routing protocols interact with new Traffic Engineering capabilities to create Interior Gateway Protocol (IGP) shortcuts. In particular, this document describes how Dijkstra's Shortest Path First (SPF) algorithm can be adapted so that link-state IGPs will calculate IP routes to forward traffic over tunnels that are set up by Traffic Engineering. 1. Introduction Link-state protocols like integrated Intermediate System to Intermediate System (IS-IS) [1] and OSPF [2] use Dijkstra's SPF algorithm to compute a shortest path tree to all nodes in the network. Routing tables are derived from this shortest path tree. The routing tables contain tuples of destination and first-hop information. If a router does normal hop-by-hop routing, the first- hop will be a physical interface attached to the router. New traffic engineering algorithms calculate explicit routes to one or more nodes in the network. At the router that originates explicit routes, such routes can be viewed as logical interfaces which supply Label Switched Paths through the network. In the context of this document, we refer to these Label Switched Paths as Traffic Engineering tunnels (TE-tunnels). Such capabilities are specified in [3] and [4]. The existence of TE-tunnels in the network and how the traffic in the network is switched over those tunnels are orthogonal issues. A node may define static routes pointing to the TE-tunnels, it may match the Shen & Smit Informational [Page 1] RFC 3906 IGP ShortCut Over MPLS LSPs October 2004 recursive route next-hop with the TE-tunnel end-point address, or it may define local policy such as affinity based tunnel selection for switching certain traffic. This document describes a mechanism utilizing link-state IGPs to dynamically install IGP routes over those TE-tunnels. The tunnels under consideration are tunnels created explicitly by the node performing the calculation, and with an end-point address known to this node. For use in algorithms such as the one described in this document, it does not matter whether the tunnel itself is strictly or loosely routed. A simple constraint can ensure that the mechanism be loop free. When a router chooses to inject a packet addressed to a destination D, the router may inject the packet into a tunnel where the end-point is closer (according to link-state IGP topology) to the destination D than is the injecting router. In other words, the tail-end of the tunnel has to be a downstream IGP node for the destination D. The algorithms that follow are one way that a router may obey this rule and dynamically make intelligent choices about when to use TE-tunnels for traffic. This algorithm may be used in conjunction with other mechanisms such as statically defined routes over TE-tunnels or traffic flow and QoS based TE- tunnel selection. This IGP shortcut mechanism assumes the TE-tunnels have already been setup. The TE-tunnels in the network may be used for QoS, bandwidth, redundancy, or fastreroute reasons. When an IGP shortcut mechanism is applied on those tunnels, or other mechanisms are used in conjunction with an IGP shortcut, the physical traffic switching through those tunnels may not match the initial traffic engineering setup goal. Also the traffic pattern in the network may change with time. Some forwarding plane measurement and feedback into the adjustment of TE-tunnel attributes need to be there to ensure that the network is being traffic engineered efficiently [6]. 2. Enhancement to the Shortest Path First Computation During each step of the SPF computation, a router discovers the path to one node in the network. If that node is directly connected to the calculating router, the first-hop information is derived from the adjacency database. If a node is not directly connected to the calculating router, it inherits the first-hop information from the parent(s) of that node. Each node has one or more parents. Each node is the parent of zero or more down-stream nodes. For traffic engineering purposes, each router maintains a list of allShow full document text