Service Domain Features
2-3
8000-A2-GB21-30
April 1998
Workstation 1 (WS1) needs to send a packet to workstation 2 (WS2). For the
packet to arrive successfully at WS2:
H There is a static route on Router A for WS2. The next hop is Router B and
the destination is WS2.
H WS1 sends a packet to Router A.
H Router A consults its routing table to determine the next hop address (i.e.,
router IP address) for WS2 because WS2 is on another network (135.1.0.0).
Now that it knows the next hop address to Router B, Router A then ARPs for
Router B. Router B receives the ARP request for its IP address and does an ARP
reply with its MAC address. After Router A receives the ARP reply, it sends the
packet to the Router B which, in turn, forwards it to WS2.
Scenario 2: With Proxy ARP
In this scenario, Router B is running the proxy ARP software, and WS2 and
Router A for WS1 are on the same network (135.1.0.0).
97-15459-02
Router B
135.1.2.6/
255.255.255.0
135.1.3.9/
255.255.255.0
135.1.3.45/
255.255.255.0
LAN A LAN B
Router A
135.1.2.3/
255.255.0.0
WS2
WS1
WS1 again needs to send a packet to WS2. This time, however, Router B is
running proxy ARP and knows that WS2 lies on LAN B on the same logical
subnetwork as Router A (135.1.0.0). Router B uses proxy ARP to maintain the
illusion that only one physical network exists. Router B keeps the location of WS2
hidden from Router A, allowing Router A to communicate as if directly connected
to WS2.
NOTE:
Router A does not need a static route entry for the WS2 route because the
two LANs appear to be one.
