Proxy ARP lets a router answer an ARP request for another host. It supplies its own MAC address, allowing the requesting router to forward the frame to the proxy router, which routes the packet onward. section 9.3.1 section 9.4
R1 forwards traffic to PC3
R1 has a directly connected static route to 192.168.3.0/24 through G0/0, so it tries to resolve PC3 at 192.168.3.11 with ARP. The request reaches R2, not PC3, because broadcasts do not cross the local network. Because R2 has a route to 192.168.3.0/24, it replies with R2 G0/0's MAC address. R1's ARP table therefore maps both 192.168.3.11 and 192.168.12.2 to the same MAC address. section 9.3.1
Important operational points:
- A router replies only when its routing table contains a route to the requested destination; otherwise, it ignores the ARP request. section 9.3.1
- Directly connected static routes depend on proxy ARP, whereas a next-hop static route lets the router resolve the next hop directly. section 9.3.1 section 9.4
- Cisco routers enable proxy ARP by default, but other vendors or configurations may disable it. section 9.3.1
