RE: split horizon with poison reverse

Thanks Joe that makes sense.

Cheers,

-Aaron.

From: Joe Astorino [mailto:joeastorino1982_at_gmail.com]
Sent: Tuesday, 31 May 2011 8:56 PM
To: Aaron Riemer
Cc: Cisco certification
Subject: Re: split horizon with poison reverse

I believe that for the received router to poison reverse the route back out
the same interface it came in on, the received route already has to be down.
In other words, if your router receives a RIP route with a metric of 16, it
will then poison reverse it back out the same interface. If it is just
receiving regular RIP routes it will not.

On Tue, May 31, 2011 at 3:54 AM, Aaron Riemer <ariemer_at_amnet.net.au> wrote:

Hey guys,

I am just going through RIP at the moment and doing some lab testing.
According to Doyle "RIP employs split horizon with poison reverse".

Take the following topology.

10.0.0.0/24 ---Router A ---192.168.0.0/24 ---RouterB----172.160.0/24

Split horizon is enabled on all interfaces. With this topology if split
horizon with poison reverse is the default then why do I not see the routers
sending back poisoned routes with debug ip rip? Is poison reverse an IOS
specific feature? I do note that split horizon is working in that routes
are not advertised out the interface they were received on.

RouterA

*Mar 1 00:05:00.731: RIP: sending v2 update to 224.0.0.9 via
FastEthernet0/0 (192.168.0.1)

*Mar 1 00:05:00.731: RIP: build update entries

*Mar 1 00:05:00.731: 10.0.0.0/24 via 0.0.0.0, metric 1, tag 0

*Mar 1 00:05:00.963: RIP: received v2 update from 192.168.0.2 on
FastEthernet0/0

*Mar 1 00:05:00.963: 172.16.0.0/24 via 0.0.0.0 in 1 hops

RouterB

*Mar 1 00:03:12.083: RIP: sending v2 update to 224.0.0.9 via
FastEthernet0/0 (192.168.0.2)

*Mar 1 00:03:12.083: RIP: build update entries

*Mar 1 00:03:12.083: 172.16.0.0/24 via 0.0.0.0, metric 1, tag 0

*Mar 1 00:03:14.791: RIP: received v2 update from 192.168.0.1 on
FastEthernet0/0

*Mar 1 00:03:14.791: 10.0.0.0/24 via 0.0.0.0 in 1 hops

/me scratches head.

Thanks,

-Aaron.

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Received on Wed Jun 01 2011 - 14:37:33 ART