UMN:CLI User Manual
V5808
230
Fig. 7.15 Proxy ARP
The host A needs the MAC address of the host D to reach the host D. Therefore, the host
A broadcasts an ARP request on the subnet A, including the V5808’s br1 interface, but
does not reach the host D. By default, the V5808 does not forward broadcasts. Since the
V5808 knows that the target address (the host D’s IP address) is on another subnet and
can reach the host D, it will reply with its own MAC address to the host A.
The proxy ARP replies that the V5808 sends to the host A. The proxy ARP reply packet is
encapsulated in an Ethernet frame with its MAC address as the source address and the
host A’s MAC address as the destination address. The ARP replies are always unicast to
the original requester. On receiving this ARP reply, the host A updates its ARP table.
From now on, the host A will forward all the packets that it wants to reach the host D to
the MAC address of the V5808. Since the V5808 knows how to reach the host D, the
router forwards the packet to the host D. The ARP cache on the hosts in the subnet A is
populated with the MAC address of the V5808 for all the hosts on the subnet B. Hence,
all packets destined to the subnet B are sent to the router. The V5808 forwards those
packets to the hosts in the subnet B.
To configure the interface to accept and respond to proxy ARP, use the following
command on Interface Configuration mode.
Enables the proxy ARP function on specific interface.
Disables the proxy ARP function.
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