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  1. Hi William,

    In my opinion, it is best practice to disable proxy ARP. In a “normal” network, it’s only helpful to solve the issue where hosts have configured the wrong subnet mask. Instead of using proxy ARP, it’s better to fix the subnet masks.

    The only reason why you might use it is if you want to do some crazy things like NAT hairpinning. For example:

    Cisco ASA NAT hairpin internal server


  2. Hello Ananth!

    MAC address learning that occurs on a switch involves the learning of the MAC addresses that are attached to the specific interface. For example, if interface Fa0/1 is connected to PC1 with MAC Address A:B:C:D:E:F, then this MAC address will be used to populate the MAC address table. The Fa0/1 interface does not need to learn its own MAC address. What happens if interface Fa0/1 is connected to interface Fa0/2 of another switch. Won’t the MAC address of Fa0/2 of that switch be included in the MAC table of the first switch? It depends.

    It is important to understand that the creation of the MAC address table in a switch is done via the Source MAC address found in the incoming frames on an interface. If the other switch is never the destination of a frame, then this MAC address will not be included in any MAC address table. MAC addresses of specific switch interfaces will not enter the MAC tables of other switches unless the switches themselves are the sources (or destinations) of frames.

    I hope this has been helpful.


  3. Hello Carlo

    Yes that is correct. In most IOS versions, proxy arp is enabled by default. This will disable it and will prevent the router from responding on behalf of another host.

    I hope this has been helpful!


  4. Hello Apiwat

    Proxy ARP is a feature of the R1 router in the topology. The changing of the S1 device to Windows 7 or any other operating system should not affect the result. Make sure that you have IP connectivity to the Windows device and that all other connectivity has been achieved, and let us know your results.

    I hope this has been helpful!


  5. Hi Apiwat,

    Proxy ARP will only work for subnets that are directly connected to your router. R1 is not going to reply to that ARP request from PC1 when it’s destined for some subnet that is behind another router.

    There is no good reason to use proxy ARP, it’s a fix for a design issue that should be fixed in your network :slight_smile:


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