[c-nsp] Uneven LACP load-balancing

[Benjamin Lovell]

This really just shot in the dark but you have CEF hash for ECMP and then etherchannel hash for link selection. I wonder if it's a weird example of polarization such that because CEF hash decided left now all traffic subject to etherchannel hash for that port-channel will resolve to one link. 

I don't know if this is true of how the CEF versus etherchannel hashing works but it fits your results.

-Ben

On Nov 10, 2010, at 12:34 PM, Brandon Ewing wrote:

> I've got a weird problem that I hope someone can shed some light on.  We
> have multiple 3560G's deployed currently, each utilizing 4 SFP's for uplink.
> The switches are configured with 2 L2 port-channels, with a different SVI in
> each port-channel pointing to our upstream router.  IE:
> 
> g0/49 + g0/51 to core A, carries Vlan 100
> g0/50 + g0/52 to core B, carries Vlan 200
> 
> Group  Port-channel  Protocol    Ports
> ------+-------------+-----------+-----------------------------------------------
> 4      Po4(SU)         LACP      Gi0/49(P)   Gi0/51(P)
> 5      Po5(SU)         LACP      Gi0/50(P)   Gi0/52(P)
> 
> 
> We have two default routes, pointing out the above vlans:
> switch#show ip cef 0.0.0.0 0.0.0.0
> 0.0.0.0/0
>  nexthop 10.10.1.241 Vlan200
>  nexthop 10.10.1.245 Vlan100
> 
> The etherchannel load-balancing method is set to src-dst-ip:
> switch#show etherc load-balance
> EtherChannel Load-Balancing Configuration:
>        src-dst-ip
> 
> EtherChannel Load-Balancing Addresses Used Per-Protocol:
> Non-IP: Source XOR Destination MAC address
>  IPv4: Source XOR Destination IP address
>  IPv6: Source XOR Destination IP address
> 
> 
> However, we are not seeing an even distribution of traffic among the 4
> ports -- each L2 etherchannel is trasmitting on only one port:
> switch#show control util
> Port       Receive Utilization  Transmit Utilization
> Gi0/49             1                    55
> Gi0/50             6                    0
> Gi0/51             1                    0
> Gi0/52             12                   57
> 
> Examination of flowstats from the core on the uplink interfaces shows a good
> mix of src/dst IPs -- so why am I getting the polarization?
> 
> Additionally, examining a test flow with the command line shows that it
> SHOULD be working, but it's not:
> 
> switch#show ip cef exact-route 172.16.79.186 192.168.42.183
> 172.16.79.186 -> 192.168.42.183 => IP adj out of Vlan100, addr 10.10.1.245
> 
> switch#test etherchannel load-balance interface po4 ip 172.16.79.186 192.168.42.183
> Would select Gi0/51 of Po4
> 
> However, g0/51 has no traffic on it, and hasn't for some time.  Can anyone
> provide some clue?  This is occuring on multiple switches, and all switches
> are running 12.2(50)SE1 ip services
> 
> -- 
> Brandon Ewing                                        (nicotine at warningg.com)
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