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RE: Cisco etherchannel question

  • From: Vinay Bannai
  • Date: Wed Oct 20 23:40:12 2004

When using EtherChannel or 802.3ad, the load balancing done by the devices
on the either end can follow completely different algorithms. One end may be
using the source or destination MAC address and the other end may be using
<source mac, destination mac> combination. Some other algorithms can go up
as far the IP header to do the load balancing. So finer the granularity of
the flow, the better the chances of getting load balance across the ports.
However, whatever mechanism they follow, they have to adhere to a rule of
NOT re-ordering packets in a flow.

It appears that the router seems to have a better load balancing than the
switch. I am not sure but the switch may have some knobs that allow you to
balance on additional headers in the header.

Vinay Bannai


-----Original Message-----
From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu]On Behalf Of
william(at)elan.net
Sent: Wednesday, October 20, 2004 7:28 AM
To: nanog@merit.edu
Subject: Cisco etherchannel question




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@elan.net





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