[c-nsp] Uneven LACP load-balancing

Benjamin Lovell belovell at cisco.com
Fri Nov 12 11:54:03 EST 2010


Following up on this. Does the 3560 support etherchannel hash on src- 
dst-mac and src-dst-ip? This should change up the hash between CEF and  
etherchannel and prevent a polarization like effect.

-Ben

On Nov 11, 2010, at 4:58 PM, Benjamin Lovell wrote:

> 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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>
>
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