Cisco 4900M Etherchannel load-balancing issue

[g.boisseau]

We have to cisco WS-C4900M with Cisco IOS Software, Catalyst 4500 L3 Switch Software (cat4500e-IPBASE-M), Version 12.2(53)SG5, RELEASE SOFTWARE (fc1).

We have four gigabit link connected between those two switches.

We have create a LACP port channel with those four ports on both switches.

Etherchannel is up and running and defined with a load-balancing method of src-dst-ip.

But when we test the load-balancing, it's not using the src-dst-ip rule with the XOR:

Switch#show platform software etherchannel port-channel 1 map ip 151.92.205.28 160.220.148.120

Map port for Ip 151.92.205.28, 160.220.148.120 is Gi2/9(Po1)

NOTE: Software forwarded traffic will use Gi2/10(Po1)

Switch#show platform software etherchannel port-channel 1 map ip 160.220.148.120 151.92.205.28

Map port for Ip 160.220.148.120, 151.92.205.28 is Gi2/11(Po1)

NOTE: Software forwarded traffic will use Gi2/10(Po1)

Is it a known issue on the XOR rule of the 4900M ?

[paolo bevilacqua]

Actually the command output indicates two different ports, 2/9 and 2/11, that indicates traffic would use both.

Note that depending on the direction of traffic, one of the two pairs (that comprise the same addresses), will never be valid for distribution.

In any case, it is better to use an algorithm that also includes port numbers, if available on your platform.

[g.boisseau]

The Etherchannel load-balancing is configured like this:

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

So (IP address A) XOR (IP address B) must give the same result as (IP address B) XOR (IP address A), because A XOR B = B XOR A, except if it's not a XOR that is used by the switch.

So in our case, the same pair of IP addresses must use the same port of the channel despite the direction.

[paolo bevilacqua]

"XOR" can be just an high-level description and the actual algorithm be more sophisticated..

What matters, is that when you repeat the command with the same pair of address in the same order, you will obtain the same output port.

[g.boisseau]

My concern is to understand what it is given by the EtherChannel Load-Balancing Configuration.

If I read " IPv4: Source XOR Destination IP address", I would expect to have a XOR as a result but it's not the case on C4900 whereas the "src-dst-ip" load-balancing is working as designed (so with a XOR) on Cisco 3750e.

[paolo bevilacqua]

Different platforms can behave differently and not everything is fully documented or intuitive.

Keep the setting in use for a time and check practical results, beside test command.