ARP: Proxy ARP

ARP still acts the same as far as the request to resolve the MAC address, but say you have a large subnet segmented between multiple routers.  Instead of hosts immediately sending traffic to their default-gateways they will ARP for the address, thinking they’re on-net.

What happens when Proxy-ARP is configured is the Router that’s segmenting the networks receives the ARP, instead of dropping the ARP, it replies with it’s own MAC address…instructing the host to send packets to him to get  to the IP they’re trying to connect to…this was useful back in the day before DHCP and allowed hosts to learn where to send their traffic to ‘by default’.

proxyarp.PNG

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