The addressing method depicted in
Figure 4-9
is used when the two
nodes reside on the same physical segment (or ring) or if they
reside on separate segments interconnected by repeaters or
bridges.
If the two nodes have different
network numbers (reside on different network segments), the
sending node must find a router on its own segment that can
forward packets to the destination node's network segment.
To
find this router, the workstation broadcasts a RIP packet
requesting the fastest route to the destination node's network
number.
This RIP request is
responded to by the router residing on the sending node's segment
with the shortest path to the desired segment; in the response,
the router includes its node number.
Sending the packet
Once the sending node receives the router's node number, it is
prepared to send packets to the destination node.
The sending node addresses these packets by placing:
the node number of the router -- the one that responded to
the RIP request -- in the destination address field of
the MAC header.
its own node number in the
source address field of the MAC header.
the
destination node's IPX address (network, node and socket
number) in the destination address fields of the IPX header.
its own IPX address in the
source address fields of the IPX header.
When a router receives a packet to be routed, it can take one of
two possible actions.
If the packet is destined for a network
number to which the router is directly connected,
the router will:
Place the destination node number from the IPX header in the
destination address field of the MAC header.
Place its own node
number in the source address field of the MAC header.
Transmit the packet.
Figure 4-10
illustrates this process.
If the router is not directly connected to the segment that the
final destination node resides on, however, it will send the
packet to the next router in the path to the destination node.
To forward the packet to another router, the router will:
Place
the node number of that other router in the destination address
field of the MAC header.
Place its
own node number in the source address field of the MAC header.
Leave the IPX header as initially set by the sending
node and sends the packet.