[c-nsp] OSPF equal cost load balancing

James Bensley jwbensley at gmail.com
Wed Aug 30 16:43:38 EDT 2017

I think two layer ECMP links are being used here, both of which are in
the IGP. Are you running MPLS over these links too?

The ME3600 is able to ECMP over any number of links as far as I know
(up to the max, which is 8 or 16) however I think the ASR920 will only
ECMP over 4 or 8 links (so not 2 as in your case). This could be the
problem here.

Could you also try to change the CEF load balancing algorithm
(assuming this is ECMP and not LAG, this won't affect a LAG):

ASR920(config)#ip cef load-sharing algorithm ?
  include-ports  Algorithm that includes layer 4 ports
  original       Original algorithm
  tunnel         Algorithm for use in tunnel only environments
  universal      Algorithm for use in most environments

If it is a LAG then on the ASR920 try to adjust these options:

ASR920(config)#port-channel load-balance-hash-algo ?
  dst-ip                 Destination IP
  dst-mac                Destination MAC
  src-dst-ip             Source XOR Destination IP Addr
  src-dst-mac            Source XOR Destination MAC
  src-dst-mixed-ip-port  Source XOR Destination Port, IP addr
  src-ip                 Source IP
  src-mac                Source MAC

If you're running MPLS over the LAG the ASR920 can hash MPLS over the
LAG and the ASR920 should hash over 2 links just fine.


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