Router 2 Router 1 Router 3 Workstation Pings Router 2 Router 1 Router 3 Workstation

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as " work in progress. " The list of current Internet-Drafts can be accessed at Abstract It is possible for link-state routing protocols to converge in link propagation time scales, that is, in tens of milliseconds. However, current deployments of ISIS[6][1], a link-state routing protocol, are not anywhere near this point. In this paper, we present some analyses of ISIS convergence by showing its behavior upon link/router failures and repairs, and its scaling properties to large networks, both in terms of number of nodes and links. We then explore changes needed in the ISIS specification and implementations to reach IGP convergence in milliseconds. Our results are based on experimentation done with ISIS, but some of the findings may apply to OSPF as well. This paper contains color figures and graphs which are missing from the ASCII version of the paper. The postscript and pdf versions of this paper can be found in the Internet-Drafts repository. 1 Motivation The theoretical limit for link-state routing protocols to reroute is in link propagation time scales, that is in tens of milliseconds. However, the current ISIS reroute times are in tens of seconds. During the reroute period, a subset of destinations are either not-reachable or are reached through non-optimal routes. It is important to close this gap between theory and implementation for several reasons. First, millisecond reroute times will lead to increased network reliability since the periods at which routes are not available/non-optimal will be shorter (one to three orders of magnitude shorter). Second, it enables multi-service traffic such as voice over IP since it decreases the number of packets dropped to tolerable levels for these services. And finally, it eliminates the need for more expensive and complex layer 2 protections schemes, such as SONET.