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looping issue where request and reply having the same source MAC and destination MAC combo

Hi all,

Having issue on my switch, it seems like a looping occur between the device it connnecting.

So there's 2 device in play: Device A (Switch) and Device B (Load Balancer).

After i doing some packet analyzing i found a funny thing on the RX capture.

The story goes like this:

Topology in simple form : host -- Device A --- Device B

01. Doing SPAN on host connecting to Device A, so test case was from host ping to Device B management IP.  No other physical port were in use except: one port connecting to the testing host, one port connecting to Device B.

02. Wireshark showing Device B replying the ECHO in the way of

source MAC : test ping host

Destination MAC :  Device B


01. In what situation will this happen? is it looping?

02. This situation cause my Device A keep on sending data or whatsoever to itself, recursively. Cause request and reply source MAC and destination MAC were the same !!!

any idea?



Cisco Employee

looping issue where request and reply having the same source MAC

You state the LB is sending an ECHO reply with source mac (host A) dest mac (LB) ? That doesnt sound like it is actually responding to the Echo request sent from the source host. Rather it is the Echo Request being looped back. Can you attach a quick snip from the wireshark capture?

Also can you tell us exactly how Device A is connected to Device B? Is it standard trunk port, etherchannel, NIC team, etc... If doing port-channel what mode?



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