Cisco etherchannel question

william(at)elan.net william at elan.net
Wed Oct 20 15:37:54 UTC 2004


Thanks for all of you who responded with info about etherchannel information. 
The core appears to be algorithm used for packet distribution among 
interfaces (which I can't change on 5500):

"The EBC performs an X-OR operation on the last two bits of the source MAC
 address and the destination MAC address. This operation yields one of
 four  results: (0 0), (0 1), (1 0), or (1 1). Each of these values points
 to a link in the Fast EtherChannel bundle"

Apparently I have bad combination of source mac addresses (I only have 7
main servers responsible for most traffic and only one destination) and 
solution in this case appears to be to manually change MAC addresses 
of some servers until I can acheive better load-balancing.

On Wed, 20 Oct 2004, william(at)elan.net wrote:

> Hi,
> 
> I have etherchannel setup between cisco 7500 router and 5500 switch.
> 
> For data going from 7500 router everything seems to be ok and data is
> well split between four interfaces with about 1/4th sent to each one
> (about 40% utilization each right now). 
> 
> But for data going from 5500 switch the split appears to be that one
> interface has 100% utilization while another one is 20% and others are
> less then 10%. So its not really splitting data on random basis to
> each interface and uses other interfaces as overflow after the main
> one. I don't like this as the one interface that is 100% full appears
> to sometimes be dropping packets on either switch or cisco router side.
> 
> I'm wondering what I can do to force 5500 to use etherchannel in similar
> way cisco 7500 does?

-- 
William Leibzon
Elan Networks
william at elan.net




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