3.8 wording

I'm little confused on 3.8 :

Modify the R1’s policy routing so that if R1 loses R5 as a CDP neighbor
traffic from R3 to R4’s Loopback0 network is rerouted directly to R4.  


Okay traffic direction could be manipulated with PBR/route-map/access-list... now Can some1 care to explain this game of words on CDP and how to use EOT tracking on that ?



P.S Just read this in soultion guide, thanks INE - I've read 3 books+DOCCD and could not find CDP correlation when it comes to PBR.



With CDP tracking for policy routing R1 looks into the CDP table to see if there is a neighbor installed with IP address that matches the next-hop value being set in the route-map. In this case the syntax

set ip next-hop

set ip next hop verify-availability

set ip default next-hop

means if there is no CDP neighbor with IP address traffic that matches this sequence will be routed to



  • unsobill - SG explains that. If ACL FROM_R3_TO_R4 is match, route-map
    is triggered. Then next-hop (of is set only if there is
    such cdp neighbor, this is due to (next-hop verify-availability). If
    no - then routing table is check, is there is no such route in RT -
    "default next-hop" of is chosen.

    route-map RELIABLE_POLICY_ROUTING permit 10
    match ip address FROM_R3_TO_R4_LOOPBACK
    set ip next-hop
    set ip next-hop verify-availability
    set ip default next-hop

  • Hi unsobill,

      The CDP thing on tracking is explained in the Command Reference Guide.

    Good luck with your studies!

  • This is referring to set ip next-hop verify-availability which uses CDP to verify if the neighbor is active or not.

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