Check out an EIGRP protocol analyzer trace and you'll see poison reverse in
action. It is more proactive then what you describe.
When Router A tells Router B "I can get to Network X," Router B tells
Router A, "I can't get to Network X."
What Router B is really saying is "I can't get to Network X except through
you, Router A. Don't use me as a feasible successor." (Though the packet
doesn't actually say all that specifically, which can be a bit confusing
when you first look at an EIGRP trace.) But it does indeed speed up
convergence when Router A loses its connection to Network X. Router A won't
try to get there via Router B.
Priscilla
At 02:57 PM 8/22/00, [EMAIL PROTECTED] wrote:
>Studying for the CCNA, I'm having trouble figuring out what the deal is with
>poisen reverse.
>
>I understand split horizon as not sending route updates back out the port
>they are received on, and I understand route poisening as specifically
>advertising a down route as bad, as opposed to just not sending any info
>about it at all. From reading in the Sybex as well as both Cisco Press ccna
>books I understand poisen reverse as sending a route poisening back out the
>port it was received in order to facilitate faster convergence and avoid
>loops in large networks.....and then they move on as if that's the end of the
>story.
>
>So Router A notices a down link on one of it's ports and sends an update to
>Router B telling it about the down route. Router B then sends an update back
>to Router A informing it of the fact. At this point the Router A in me wants
>to say, "No Kidding it's down, I just told YOU that, why are you bothering me
>with this information."
>
>There must be something basic I am missing here, such as just what is Router
>A doing with the poisen reverse update it gets from Router B telling it it
>knows the route is bad.
>
>Any comments appreciated.
>
>Joe
>
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Priscilla Oppenheimer
http://www.priscilla.com
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