3-13 Proxy ARP ConfigurationWhen configuring proxy ARP, go to these sections for information you are interested in:z Proxy ARP Overviewz Enabling Proxy ARPz Displaying and Maintaining Proxy ARPProxy ARP OverviewIf a host sends an ARP request for the MAC address of another host that actually resides on anothernetwork (but the sending host considers the requested host is on the same network) or that is isolatedfrom the sending host at Layer 2, the device in between must be able to respond to the request withthe MAC address of the receiving interface to allow Layer 3 communication between the two hosts.This is achieved by proxy ARP. Proxy ARP hides the physical details of the network.Proxy ARP involves common proxy ARP and local proxy ARP, which are described in the followingsections.The term proxy ARP in the following sections of this chapter refers to common proxy ARP unlessotherwise specified.Proxy ARPA proxy ARP enabled device allows hosts that reside on different subnets to communicate.As shown in Figure 3-1, Switch connects to two subnets through VLAN-interface 1 and VLAN-interface2. The IP addresses of the two interfaces are 192.168.10.99/24 and 192.168.20.99/24. Host A andHost B have the same prefix 192.168.0.0 assigned and connect to VLAN-interface 1 andVLAN-interface 2, respectively.Figure 3-1 Application environment of proxy ARPBecause Host A considers that Host B is on the same network, it directly sends an ARP request for theMAC address of Host B. Host B, however, cannot receive this request because it locates in a differentbroadcast domain.
