Arp Proxy; Important Considerations; Example - 3Com 4007 Implementation Manual

ARP Proxy

Important
Considerations

Example

ARP proxy allows a host that has no routing ability to determine the MAC
address of a host on another network or subnet.
When ARP proxy is enabled and a workstation sends an ARP request for a
remote network, the module determines if it has the best route and then
answers the ARP request by sending its own MAC address to the
workstation. The workstation then sends the frames for the remote
destination to the module, which uses its own routing table to reach the
destination on the other network.
Consider the following issues with ARP proxy:
Do not use ARP proxy if you are using VLSMs because ARP proxy
works by seeing the entire network configuration as one network.
ARP proxy increases ARP traffic to handle the increased mapping of IP
addresses to MAC addresses.
In the following example, Server A cannot use the router as a gateway to
Server B (if ARP proxy is disabled) because Server A has its subnet mask
set to broadcast (using ARP) its IP network address as 158.101.0.0, while
the IP network address of the router is 158.101.1.0.
However, if the router has ARP proxy enabled, the router answers the
request of Server A with its own MAC address — thus, all traffic sent to
Server B from Server A is addressed to the corresponding IP interface on
the router and forwarded appropriately.
ARP Proxy 375