[c-nsp] OSPF equal cost load balancing

[CiscoNSP List]

AAh - Thank you James!  So the ASR920 will not ECMP over 2 links, it requires 4...that would explain the difference between egress/ingress (and why the 920 is not working particularly well!)


Yes, this is ECMP, not LAG - So changing the load sharing algorithm can only be done globally (As I tried to do it under the individual interfaces, and was only presented with per dst as an option)


(config-if)#ip load-sharing ?
  per-destination  Deterministic distribution


So, changing globally will potentially cause a service disruption? (May need to do this in maintenance window) - Do you suggest "include-ports" as a possible candidate?


#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

And yes, we are running MPLS over these links (But not a LAG as mentioned) - So does your comment re MPLS hasting still apply to our setup, or only to a LAG?


Thanks again for your response - Extremely helpful!


________________________________
From: cisco-nsp <cisco-nsp-bounces at puck.nether.net> on behalf of James Bensley <jwbensley at gmail.com>
Sent: Thursday, 31 August 2017 6:43 AM
To: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] OSPF equal cost load balancing

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.

Cheers,
James.
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