Foundry NetIron M2404C and M2404F Metro Access Switches
Configuring Routing Information (Rev. 03)
Configuring Proxy ARP
© 2008 Foundry Networks, Inc.
Page 36 of 48
The proxy ARP reply packet is encapsulated in an Ethernet frame with the router MAC address as
the source address and Host A’s MAC address as the destination address. The ARP replies are
always unicast to the original requester.
On receiving this ARP reply, Host A updates its ARP table as follows:
IP Address
MAC Address
122.1.30.20 00:12:F2:05:36:80
From now on Host A will forward all the packets that it wants to reach Host D to the MAC address
of the router. Since the router knows how to reach Host D, the router forwards the packet to Host D.
The ARP cache on the hosts in Subnet A is populated with the MAC address of the router for all
the hosts on the Subnet B. Hence all packets destined to Subnet B are sent to the router. The router
forwards those packets to the hosts in Subnet B.
The ARP cache of Host A is given below:
IP Address
MAC Address
122.1.30.20 00:12:F2:05:36:80
122.1.30.10 00:12:F2:05:36:80
122.1.1.1 00:12:F2:05:36:80
122.1.1.20 00:C0:03:FD:50:04
Note that Multiple IP addresses are mapped to a single MAC address (the router MAC address),
indicating that proxy ARP is in use.
The Foundry Networks router IP interface should be configured to accept and respond to proxy
ARP. This is disabled by default. Proxy ARP can be enabled on a per IP interface basis with the IP
Interface Configuration command
ip arp proxy
, as follows:
device-name
#
configure terminal
device-name
(config)#
interface sw1
device-name
(config-if
sw
1)#
ip address 122.1.1.1/24
device-name
(config-if
sw
1)#
ip arp proxy