[c-nsp] interesting ASR 9k bgp multipath issue

[John van Oppen]

so, I have some internally anycasted prefixes (DNS resolvers) as well as bgp maximum paths set to allow both ibgp and ebgp multipath.   Oddly, as you can see below the multipath appears to think two paths are identical even when they have different IGP metrics (path #1 and path #2), any idea if this is a bug or how to fix it?    Obviously if the IGP cost is the same it should load share, but if not it really should not be doing what is shown below since the paths are not equal.

This behavior does not happen on the other cisco platforms we use, they only multipath to destinations that have the same IGP cost or are locally connected via EBGP with the same policy.    This is not a huge issue since i can work around it, but it is annoying as it should not be happening.  

If anyone has ideas of knobs to tweak that would be awesome as my google foo is turning up precious little that is applicable.


example route:



RP/0/RSP0/CPU0:cr2-sea-b#show bgp ipv4 unicast 208.76.152.9
Sun Mar 30 08:54:24.730 UTC
BGP routing table entry for 208.76.152.9/32
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker           53174704    53174704
Last Modified: Mar 30 07:37:05.725 for 01:17:19
Paths: (3 available, best #1)
  Advertised to update-groups (with more than one peer):
    0.1 0.14 
  Path #1: Received by speaker 0
  Advertised to update-groups (with more than one peer):
    0.1 0.14 
  64524, (Received from a RR-client)
    208.76.153.79 (metric 16) from 208.76.153.79 (208.76.153.79)
      Origin incomplete, metric 10, localpref 200, valid, internal, best, group-best, multipath, import-candidate, import suspect
      Received Path ID 0, Local Path ID 1, version 53174704
      Community: 11404:800
  Path #2: Received by speaker 0
  Not advertised to any peer
  64524
    208.76.153.79 (metric 16) from 208.76.153.116 (208.76.153.79)
      Origin incomplete, metric 10, localpref 200, valid, internal, import suspect
      Received Path ID 0, Local Path ID 0, version 0
      Community: 11404:800
      Originator: 208.76.153.79, Cluster list: 208.76.153.116
  Path #3: Received by speaker 0
  Not advertised to any peer
  64524
    208.76.153.118 (metric 2546) from 208.76.153.118 (208.76.153.118)
      Origin incomplete, metric 10, localpref 200, valid, internal, multipath, import-candidate, import suspect
      Received Path ID 0, Local Path ID 0, version 0
      Community: 11404:800
RP/0/RSP0/CPU0:cr2-sea-b#


John van Oppen
Spectrum Networks
Direct: 206-973-8302
Main: 206-973-8300