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Latest post 03-07-2017 2:08 PM by major133. 3 replies.
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  • 03-06-2017 8:30 PM

    changing layer 2 address





    as you see into this picture

    when pc1 send frame to pc2 , src mac=0000.0000.0003 dst mac =0000.0000.0004

    but why sw don`t change layer 2 mac address to be outgoing port f0/0

    so when frame sent out from sw wiill be like this

    src mac=0000.0000.0003 dst mac=0000.0000.0002 ?

    • Post Points: 35
  • 03-06-2017 9:26 PM In reply to

    Re: changing layer 2 address


    • Post Points: 5
  • 03-06-2017 9:31 PM In reply to

    • rriker
    • Top 50 Contributor
    • Joined on 02-21-2013
    • Milwaukee, WI
    • Elite
    • Points 7,050

    Re: changing layer 2 address

    Simple, a switch that connects to endpoints (PCs) together on a common VLAN, as depicted in your picture, the switch would learn the MACs of PC1 and PC2. The CAM or MAC Address table would get populated with a MAC to Port binding, the port that learned the MAC address. So when PC1 would send a frame out to the switch, the switch looks at the layer 2 header and sees the destination as PC2, looks in its CAM table and finds an entry. The switch then knows which port to send the frame out to.

    If you were Layer 3 Routing, then the layer 2 header would get stripped off at the layer 3 gateway and would be rebuilt as the layer 3 gateway would forward the frame out the exit interface to the destination. Layer 2 headers are only maintained inside the same broadcast domain, once traffic exits the broadcast domain, the layer 2 header needs to be rewritten on a per hop basis. 



    Rob Riker, CCIE #50693, CCNP Service Provider, VCP5-DCV

    • Post Points: 20
  • 03-07-2017 2:08 PM In reply to

    Re: changing layer 2 address

    Hi rob

    thank you very much


    • Post Points: 5
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