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5204 Views 2 Replies Latest reply: May 3, 2010 5:10 PM by zeroone RSS

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Arp table

May 3, 2010 3:53 PM

zeroone 296 posts since
Jan 13, 2010



I have a question about arp table. let's say we have the following setup.


R0 and R1 are on point to point wan link. R1 is connected to Sw1 which is connected to 2 pcs within same subnet. The network is up for a few days and have communication before. I would like to know how R1 arp table and Sw1 arp table look like.


Will Ri arp has only one entry for the link connected to sw1 or will R1 has entries for 2 pcs and switch links?


What would sw1 arp table look like?


Please educate me.


Thank you in advance.

  • Keith Barker - CCIE RS/Security, CISSP 5,327 posts since
    Jul 3, 2009
    Currently Being Moderated
    1. May 3, 2010 4:50 PM (in response to zeroone)
    Re: Arp table

    htoonthura -


    I did a video to answer your specific question, using this topology:


    ARP tables-2.jpg


    On the serial link, there will be NO ARP information, as ARP isn't used on serial interfaces for L3 to L2 resolution.  The video shows the final arp cache on R1, PC0, and PC1.


    There would be no ARP cache on the switch, as it is only a L2 device used in this scenario.  If we looked at the MAC address table on the switch, it would show the MAC address of the router associated with Fa0/1, the MAC address of PC0 associated with Fa0/2, and the MAC address of PC1 associated with Fa0/3.


    Switch#show mac-address-table
              Mac Address Table


    Vlan    Mac Address       Type        Ports
    ----    -----------       --------    -----


       1    0001.973e.6301    DYNAMIC     Fa0/1
       1    0009.7cb0.042d    DYNAMIC     Fa0/2
       1    000a.41c7.a737    DYNAMIC     Fa0/3


    The full video ( about 4 minutes long ) is here:


    I just published it, and it is being processed right now.


    Best wishes,




    PS the PT file is attached.

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