[c-nsp] Load balancing on portchan (4500X->ASR1006)

[Adam Baxter]

I ran into a similar problem lately with a 4500X VSS Setup.
Multichassis Etherchannel will not send traffic over the VSL Link and
out of the Secondary Switch. It will only send it out of the Primary
Switch.

from: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4500/15-1-2/XE_340/configuration/guide/config/vss.html

At the VSS, an MEC is an EtherChannel with additional capability: the
VSS balances the load across ports in each switch independently. For
example, if traffic enters the VSS active switch, the VSS selects an
MEC link from the VSS active switch. This MEC capability ensures that
data traffic does not unnecessarily traverse the VSL.

On 3 June 2017 at 01:21, CiscoNSP List <CiscoNSP_list at hotmail.com> wrote:
> Hi Everyone - Have a 4 port etherchan between ASR1006/4500X(In VSS) - Tried virtually all the load-balancing options on the 4500X, but port "1" in the portchan group always gets majority of traffic share.
>
>
> Links are:
>
>
> ASR1006      4500X (2)
>
> 0/0/3            1/1/4
>
> 1/0/0            1/1/16
>
> 1/0/3            2/1/4
>
> 2/0/0            2/1/16
>
>
> src/dst ip - I get both ports on "primary" 4500X being primarily used (1/1/4 getting the most)
>
> src/dst mac - I get a bit of a better load spread, but 2/1/4 gets very little traffic, and again 1/1/4 gets the most
>
> src/dst port - 1/1/4 gets the most, 2/1/16 gets a lot more (ingress), 2/1/4, very little
>
>
> The portchan peak usage is 2 to 2.5Gb/sec, but would do more, as it is being limited by the load-balancing....i.e 1/1/4 will max out at 1G/sec    (We have a very bursty traffic.....SP - So mix of Inet/L3VPN/backup/replication etc)
>
>
> If anyone has some suggestions on how to achieve a better(more even) traffic spread, it would be greatly appreciated....Migrating to 10Gb is what we plan to do, but am interested in anyones comments on why 1/1/4 is used so heavily regardless of the load-balancing algorithm used (Assuming it is because it is the "first" port....spanning tree  probably preferring this port?)....the ASR1006 only has 2 load-balancing options flow-based or vlan-manual......lol and I dont have any interest in setting up manual vlan load-balancing 😉)
>
>
> Thanks
>
>
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