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

[yong khang NG]

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

Qusstion

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?

Thanks

Noel

[Dale Miller]

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?

Thanks,

Dale