Cisco etherchannel question


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?

Let's move this to the cisco-nsp alias since
it's a vendor specific question.


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.

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