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

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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 10.1.1.1 10.1.1.2
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.

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About the Author:

A Senior Network and Security consultant and the company Chief Technology Officer, is an expert in the design and operation of networking systems essential to supporting complex requirements. Amante Bustamante has over 15 years of Technical IT experience with a specialization in Network and Network Security integrations.
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