[c-nsp] OSPF equal cost load balancing

CiscoNSP List CiscoNSP_list at hotmail.com
Thu Aug 31 01:14:48 EDT 2017 

Hmm - Well this is just not wanting to play nicely at all....


Ive added another 2 links (Now 4 total), all equal cost - Egress load (From ASR920->ME3600) went from Gi0/0/22 doing 950M/sec,  Gi0/0/23 doing 5-10Mb/sec, to Gi0/0/20 now taking all the load...


So, we have gi0/0/20,21,22,23 connected to the "corresponding" ports on the ME3600 (gi0/20,21,22,23)


Now gi0/0/20 is doing 970Mb/s a sec.....Ive tried every combination of load-sharing in global conf, and they initially make a bit of a difference (i.e. the other ports will do 5-10Mb/sec each), but then revert back to Gi0/0/20 being maxed out.


 #show int gigabitEthernet 0/0/20 | inc 30 sec
  30 second input rate 90190000 bits/sec, 14882 packets/sec
  30 second output rate 969898000 bits/sec, 144872 packets/sec
 #show int gigabitEthernet 0/0/21 | inc 30 sec
  30 second input rate 74069000 bits/sec, 13780 packets/sec
  30 second output rate 1778000 bits/sec, 312 packets/sec
 #show int gigabitEthernet 0/0/22 | inc 30 sec
  30 second input rate 96760000 bits/sec, 15992 packets/sec
  30 second output rate 3067000 bits/sec, 444 packets/sec
 #show int gigabitEthernet 0/0/23 | inc 30 sec
  30 second input rate 103174000 bits/sec, 16690 packets/sec
  30 second output rate 395000 bits/sec, 101 packets/sec


Help?  😊



________________________________
From: CBL <alandaluz at gmail.com>
Sent: Thursday, 31 August 2017 1:13 PM
To: CiscoNSP List
Cc: James Bensley; cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] OSPF equal cost load balancing

What if you were to setup four BDIs running OSPF/MPLS across these two physical interfaces. Two BDIs per physical interface. Would that make ECMP work correctly using an ASR920?

We're going to be in the same boat soon too.. ASR920's on both sides with OSPF across two physical paths and worried about load sharing. Most of our traffic is MPLS xconnects traversing these links (licensed backhauls).


On Wed, Aug 30, 2017 at 6:35 PM, CiscoNSP List <CiscoNSP_list at hotmail.com<mailto:CiscoNSP_list at hotmail.com>> wrote:
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<mailto:cisco-nsp-bounces at puck.nether.net>> on behalf of James Bensley <jwbensley at gmail.com<mailto:jwbensley at gmail.com>>
Sent: Thursday, 31 August 2017 6:43 AM
To: cisco-nsp at puck.nether.net<mailto: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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