Priscilla, Isn't there a difference between poison reverse (which is a variation on split horizon) and route poisoning? I thought poison reverse took place each time a route was learned. For example, router A advertises network 1 to router B. Router B immediately poison reverses the route to router A. Route poisoning only happens in the triggered fashion that you described in your post. Or so I thought.
Thanks, Scott Priscilla Oppenheimer wrote: > > Cisco does actually support a form of poison reverse with RIPv1 > and v2. > It's not proactive, but it still fits the definition. > > When a router loses a route to a network behind it, it > announces that it > can't get to the network by sending a RIP update that lists the > network > with a distance of 16. The router does this quickly, without > waiting for > the next update timer. It sends a triggered update. > > I have observed that other routers then also say, "hey don't > use me to get > there either." These are routers that never could have gotten > there anyway > without the help of the other router. Their only path was in > the reverse > direction from the networks that they advertise. > > An example might help: > > ---network1----Router A-----network 2------Router B-----network > 3--- > > Router A loses its route to network 1. Router A sends a > triggered update > listing network 1 as unreachable (hop count = 16). Router B > then also sends > an update listing network 1 as unreachable (hop count = 16). > That could be > considered a poison reverse feature. > > Note that this isn't as proactive as some forms of poison > reverse. If this > were EIGRP, for example, as soon as Router A announced it could > get to > network 1, Router B would send an update saying its distance to > network 1 > is infinity (delay = max). It proactively tells Router A not to > ever use > Router B to get to network 1. Router B says it is not a > feasible successor > for that network. That's definitely poison reverse. Cool, eh? > > Bottom line: Cisco's implementation of RIP (and of course, > EIGRP) has > always been a bit more advanced than the textbook descriptions > of a > distance-vector algorithm. > > Priscilla > > At 11:07 PM 1/27/02, Pierre-Alex GUANEL wrote: > >Cisco does not seem to support poison reverse for RIP and RIP > version 2. > > > >Do you know network vendors who do? > > > >Pierre-Alex > ________________________ > > Priscilla Oppenheimer > http://www.priscilla.com > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=33468&t=33402 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
