ICX35-HWC ♦ Industrial Cellular Gateway
Proxy ARP
3G/4G LTE
User Manual
ProSoft Technology, Inc.
Page 124 of 127
13
Proxy ARP
Proxy ARP is a technique in which a proxy server on a given network answers the
Address Resolution Protocol (ARP) queries for an IP address that is not on that
network.
The proxy is aware of the destination location and offers its own MAC (Media Access
Control) address as the (ostensibly final) destination. The traffic directed to the proxy
address is typically routed by the proxy to the intended destination via another
interface or tunnel.
The process results in the proxy server responding with its own MAC address to an
ARP request for a different IP address for proxy purposes.
Proxy ARP can be used when clients are on different physical networks but
configured as if they are all on the same subnet. It can be used to create a subnet
effect without changing the network configuration of the devices.
13.1
Proxy ARP Sample Topology
The example above has two subnets:
10.1.1.0 /24
and
10.2.2.0 /24
. The routers
(ICX35-HWC) are connected to both subnets via WAN connections. One ICX35-
HWC network includes two hosts (H1 and H2), and the other ICX35-HWC network
includes a server (S1).
The H1 host has a /24 subnet mask and the H2 host has a /8 subnet mask. When
H1 tries to reach the S1 server at 10.2.2.100, the following occurs:
1)
H1 compares its IP address and subnet mask to the S1 server IP address
(10.2.2.100) and decides that the server is on another subnet.
2)
H1 sends the packet to its default gateway (10.1.1.254).
3)
H1 checks its ARP table to see if there is an entry for 10.1.1.254, if not it will
send an ARP request.
4)
The ICX35-HWC router will respond to the ARP request, sending its MAC
address of its Fast Ethernet (LAN) interface.
