5.2 -- MSDP originator ID required?

I understand why the solution has "ip msdp originator-id loopback x" -- to avoid possible duplicate router IDs in MSDP messages due to the loopback interface being anycasted -- but is this required for this answer to be correct?


My understanding is if there's only 2 MSDP members, a relaxed set of rules is used and the originator ID is ignored for loop prevention -- even if it a duplicate.


Furthermore, MSDP tested out ok (but I did not force it to be a duplicate ID -- the particular non-msdp loopback was numerically higher anyways so it wouldn't have used a duplicate RID).


For these two reasons (although I can't say which), I think this should still be correct without originator ID specified?  Or is it wrong?


  • Configuring MSDP I usually run the "ip msdp originator-id" to set up the loopback manually and make sure that I have the peer "under control". Especially when you have to set up ANYCAST using different loopback interfaces.

  • Hi pc500,

    I used the same solution, and it worked fine for me too.

    However I dont think msdp originator-id has something to do with router-id in MSDP. As far as I remember, the originator-id forces the MSDP peer to change the RP advertised in the Source Advertisement (SA) messages : the SA does not contain just the (S,G) information, but also the address of the RP on which that (S,G) registered. The originator-id will override the RP address information with whatever you want it to be. Note that only the RP that orignated the SA can modify the RP address in the SA message : subsequent MSDP peer that may forward the SA further are not allowed to modify it.


    But you are right that since in this scenario each MSDP router has only one peer, then it will accept whatever SA it receives. With more peers, more complicated rules apply to determine if an SA should be accepted or not.



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