is mac address changed when being routed?

Hello ~: i have a confusing concept problem that i need help !! there are two switches, and those are connected to Router A. and please look at this following facts: switch A has connection to host A. switch B has connection to host B.

Like this: host B | Router A __Switch B | switch A __host A

My question is "What will be the source mac address of the frames that hostA receives from hostB?"

I answered this question as "The Mac address of router interface.", but the correct answer was "The Mac address of hostB mac address.."!!!!

How come..? I hope this question has wrong answer itself !!!

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You were correct. MAC addresses pass through switches, but not through routers.

Reply to
Barry Margolin


it's hard to tell from the textual diagram, but the key is how the switches are connected to each other, and to the router - ??

ie - if they all are on the same ethernet and can "see" each other directly, then the MAC would just go across from one switch to another.

However - if the switches are connected to TWO interfaces on the router, then the frames would have to pass THRU the router MAC interfaces.

Also - even if they all are on the same physical segment, if the "transmission" is using a routed protocol like TCP/IP between two subnets on the same general infrastructure, then the router again would have to route the packets, and the Ethernet frames would have the router MAC address.

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