R3303-HP HSR6800 Routers Layer 3 - IP Services Configuration Guide

11
Configuring proxy ARP
Overview
Proxy ARP enables a device on a network to answer ARP requests for an IP address not on that network.
With proxy ARP, hosts on different broadcast domains can communicate with each other as they do on
the same network.
Proxy ARP in this chapter refers to the common proxy ARP. It allows communication between hosts that
connect to different Layer-3 interfaces and reside in different broadcast domains.
Proxy ARP
A proxy ARP enabled device allows hosts that reside on different subnets to communicate.
As shown in Figure 4,
Router connects to two subnets through GigabitEthernet 3/0/1 and
GigabitEthernet 3/0/2. The IP addresses of the two interfaces are 192.168.10.99/24 and
192.168.20.99/24. Host A and Host B are assigned the same prefix 192.168.0.0. Host A connects to
GigabitEthernet 3/0/1 and Host B connects to GigabitEthernet 3/0/2.
Figure 4 Application environment of proxy ARP
Because Host A and Host B have the same prefix 192.168.0.0, Host A considers that Host B is on the
same network, and it broadcasts an ARP request for the MAC address of Host B. However, Host B cannot
receive this request because it is in a different broadcast domain.
You can enable proxy ARP on GigabitEthernet 3/0/1 of the router so that the router can reply to the ARP
request from Host A with the MAC address of GigabitEthernet 3/0/1, and forward packets sent from
Host A to Host B. In this case, the router acts as a proxy of Host B.
A main advantage of proxy ARP is that you can enable it on a single router without disturbing routing
tables of other routers in the network. Proxy ARP acts as the gateway for hosts that are not configured with
a default gateway or do not have routing capability.
Enabling proxy ARP
You can enable proxy ARP in VLAN interface view/Layer 3 Ethernet interface view/Layer 3 Ethernet
subinterface view/Layer 3 aggregate interface view/Layer 3 aggregate subinterface view.
To enable proxy ARP: