Equal Load on Etherchannel?

jcmattos1 · ‎03-07-2007

We have an etherchannel set up between 2 6509's running CATOS @ L2 and noticed that traffic patterns is heavily unequal on one link its consistently @ 30% utiliztion while the other link is 70%. The distribution method both sides is (ip both). I attached some etherchannel info as well...Any ideas?

kcoley · ‎03-07-2007

The EtherChannel Load Balancing algorithm uses the lower bits of either the IP or MAC address. You do not say whether you use src-ip, dst-ip, or src-dst-ip, which is the XOR of both the source and destination IP address. Regardless of which option you use, the list of addresses are hashed and distributed across the channels. Normally, the list of addresses is statistically evenly distrubuted. However, in some cases, such as lab environments (i.e. testing) the addresses do not vary enough to make the load balance algorithm work exactly even. My suggestion is to try one of the other methods and see if you get better distribution across your channels.

jcmattos1 · ‎03-08-2007

Thx for the detailed explaination. I also noticed a session option in the distribution method, would this be a better option than my current config (ip both)?

glen.grant · ‎03-07-2007

The only thing you can do is play around with the etherchannel load balance command on both sides of the channel and see if you can get it to even out more . It will never be totally equal and depends on a variety of factors .

richhill · ‎03-09-2007

With a 6509, you can use any of the following to determine which link a traffic flow will use:

Router(config)# port-channel load-balance {src-mac | dst-mac | src-dst-mac | src-ip | dst-ip | src-dst-ip | src-port | dst-port | src-dst-port}

I'd say src-dst-port will probably be the closest to random, since source port is random.

More information:

http://www.ciscosystems.com/en/US/products/hw/switches/ps708/products_configuration_guide_chapter09186a0080160a03.html