3Com S7902E, Configuration Manual

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Proxy ARP Configuration
When configuring proxy ARP, go to these sections for information you are interested in:
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Proxy ARP Overview
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Enabling Proxy ARP
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Displaying and Maintaining Proxy ARP
Proxy ARP Overview
If a host sends an ARP request for the MAC address of another host that actually resides on another
network (but the sending host considers the requested host is on the same network) or that is isolated
from the sending host at Layer 2, the device in between must be able to respond to the request with the
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 following
sections.
The term proxy ARP in the following sections of this chapter refers to common proxy ARP unless
otherwise specified.
Proxy ARP
A proxy ARP enabled device allows hosts that reside on different subnets to communicate.
As shown in Figure 2-1 , Router connects to two subnets through Vlan-interface1 and Vlan-interface2.
The IP addresses of the two interfaces are 192.168.10.99/24 and 192.168.20.99/24. Host A and Host B
have the same prefix 192.168.0.0 assigned and connect to Vlan-interface1 and Vlan-interface2,
respectively..
Figure 2-1 Application environment of proxy ARP
Because Host A considers that Host B is on the same network, it directly sends an ARP request for the
MAC address of Host B. Host B, however, cannot receive this request because it locates in a different
broadcast domain.