Layer 2 Tracing for (6500, 7609, 4500) Cisco Switches

In a 6509, 7609 or any Chassis based Cisco switch, to determine where the switch forwards a Source and Destination pair to an actual port in a Port-channel/Etherchannel do the following commands:

Note: Doesn’t apply to Nexus switches.

First enter console for switch:

port-channel hash
Switch# remote login switch
Trying Switch ...
Entering CONSOLE for Switch

Then enter the following command:

port-channel hash
Switch-SP# test etherchannel load-balance interface port-channel 1 ip
Computed RBH: 0x6
Would select Gi2/1 of Po1

Based on the hash computation, the switch forwards traffic of the Src Dst pair to port Gi2/1.

This is a good tool to use if for some reason a particular port is dropping packets between the src and dst pairs.