Posted on January 8, 2019 9:46 pm
 |  Asked by Frank Bulk
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We have two Arista 7504’s, each with a downstream-facing LAG into the same Cisco 7600-series router. Both were flat-lining around 10 Gbps, so thinking that perhaps it was the downstream router, we spread the traffic around by adding a fourth 10G to each LAG. Yet we’re flat-lining around the same value — adding that fourth LAG member made no perceptible difference.
There are no deferred or output discards on the port-channel or individual ports, so my remaining thought is that there is some kind of rate-limiting going on in the Aristas that we can’t see.
Is there anything that needs to be done to a port-channel to get beyond the 10 Gbps mark? Are there any other counters we should be looking at?
If the issue was the downstream router I would be expecting to see the Aristas keep pushing traffic out but ingress discards on the downstream router … but I’m not seeing that.


Hi Frank,
Do you know where the traffic in coming from and to?
What are the breakout between ingress and egress on these links? Is you “south” the LAG egress and “north” the LAG ingress?
What MTU have you got on these interfaces (check with “show interface Ethx,y,z)
You seem to reach 9.38Gbps or 10.78Gbps. If you exceed 10Gbps then you are not limited to a single LAG member, but maybe most of the traffic goes through a single member.

What hashing distribution do you have on these links. Check with these commands, and provide the outputs:
show port-channel summary
show port-channel traffic

What is your traffic profile:
– source/destination MAC address (is everything between just 2 routers point-to-point, so invariant Layer2?)
– source/destination IP address
– L4 ports (mixed Internet traffic?)

If you have some imbalance, is there a high proportion of Multicast or Broadcast?

If it is mainly Unicast and unluckily get polarised onto the same link member, then maybe you can tune the hashing to bring more entropy.


(Alexis Dacquay at January 15, 2019 4:48 pm)

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