validate-update-source

From: Tim Chan (timanji@yahoo.com)
Date: Tue Aug 22 2006 - 06:24:53 ART


My understanding of the RIP "validate-update-source" command was that the router will assure that the source IP address of incoming updates matches the network of the received interface, right?

So can someone explain why this is needed when one side of a PPP link is getting it's IP address
from a dhcp server? (Or even being assigned from the remote peer?) It's the same subnet, so why
is the update source validation failing?

Until I add the "no validate-update-source" command, R4 will send RIP routes to R5, but refuses
 accept any.

R4:
interface serial 0/0
  encap ppp
  ip address negotiated
!
router rip
  ver 2
  network 139.1.0.0

R5:
interface serial 0/0
  encap ppp
  ip add 139.1.45.5 255.255.255.0
  peer default ip address 139.1.45.4
!
router rip
   ver 2
   network 139.1.0.0

In case you're interested, this is from IEWB Vol I - Lab 13.

Please explain....thanks!
-tim



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