Source MAC changes on routers

Unanswered Question
Oct 27th, 2009

Hi all:

Is there any command that can be applied to routers in order to somehow keep original source MACs from LAN and not changing it when routing packets to a WAN?



I have this problem too.
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walter.perera Tue, 10/27/2009 - 11:40


Thanks for replying!

In order to let things clear, let me put an example (I know this could be quite stupid, but I have to report this to my boss :) )

On a LAN, a PC (A) sends a packet to another PC (B)on another LAN. Both LANs are connected thru a WAN link, with 2 routers). As packet goes thru Router A, this router will change PC A MAC address to its own MAC, and send it to Router B.

There is no command to avoid this and send PC A source MAC address unmodified thru WAN link to PC B, correct?

Thanks (specially for the patience)


Lucien Avramov Tue, 10/27/2009 - 11:44

this is how switching works :) hence this is a no.

There is no command to achieve that or it will challenge the switching design basically.

What are you REALLY trying to achieve?

walter.perera Tue, 10/27/2009 - 12:06

Hi all:

Let me give you the context. We are using Cisco Contact Center with call recording and monitoring. It seems that it does not work when sending packets in different LANs thru a WAN link. The problem is that for recording, the system uses the source MAC address of the softphone (in this case, the PC) and that is changed in the routers.

I hope this clarifies situation.

Thanks to all for your help!



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