NANOG Meeting Presentation Abstract

ISIS Routing on the Qwest Backbone: a Recipe for Subsecond ISIS Convergence
Meeting:	NANOG24
Date / Time:	2002-02-12 9:00am - 9:30am
Room:	Grand Ballroom
Presenters:	Speakers: Cengiz Alaettinoglu, Packet Design Cengiz Alaettinoglu ([email protected]) is a member of the Technical Staff at Packet Design. He is currently working on scaling and convergence properties of both inter-domain and intra-domain routing protocols. He was previously at the USC Information Sciences Institute, where he worked on the Routing Arbiter project. Cengiz co-defined the Routing Policy Specification Language along with the protocols to enable a distributed, secure routing policy system. Steve Casner, Packet Design Stephen Casner worked on packet audio and video for 27 years, going from the ARPAnet through the MBone. This was first in the academic setting at USC/ISI, then going commercial at Precept Software and Cisco Systems. Now he is applying some of the same techniques for network performance measurement at Packet Design.
Abstract:	Routing \"convergence\" time, or the delay to reroute, is often cited as one of the key limitations for currently deployed IP networks to provide new services and scale to larger sizes. In this talk, we present an analysis of ISIS routing protocol behavior in one ISP network to demonstrate where the problems lie and how to fix them. This analysis is based on ISIS packet traces collected over multiple week-long periods on several major ISP backbone networks. The analysis focuses on two aspects. First, by observing the number of link-state packets generated and analyzing how many represent real physical changes, we show that only a few routers and links are responsible for the majority of the churn. Some of the links, when they fail, become unstable and cause continuous churn. Second, we analyze in detail the sequence of events and delays that result in convergence taking multiple seconds. We correlate the routing state learned from tracing ISIS routing packets with observations of the effects of routing upon a continuous stream of UDP test traffic while the convergence progresses. This allows us to detect link failures very quickly and to see precisely when the route changes. We have observed that during a single convergence event our stream was first black-holed, then sub-optimally routed, then looped, and finally converged to the new, optimum route. All of these steps took several seconds due to link failure detection times, link-state packet propagation times, and the surprising effect of some of the ISIS timers. By combining fixes for these problems with the results of our earlier lab experiments (as reported at NANOG 20), we conclude with a recipe for achieving subsecond IGP convergence in networks such as this ISP\'s all point-to-point core network.
Files:	Cengiz Alaettinoglu Presentation(PDF) ISIS Routing on the Qwest Backbone: a Recipe for Subsecond ISIS Convergence
Sponsors:	None.

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NANOG24 Abstracts

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