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Key Concepts 425
Sending Node’s Responsibility
When sending and destination nodes have the same network number,
the sending node addresses and sends packets directly to the destination
node. If sending and destination nodes have different network numbers,
as in Figure 76, the sending node must find a router on its own network
segment that can forward packets to the destination node’s network
segment.
To find this router, the sending node broadcasts a RIP packet, requesting
the best route to the destination node’s network number. The router on
the sending node’s segment that has the shortest path to the destination
segment responds to the RIP request. The router’s response includes its
network and node address in the IPX header. After the sending node
determines the intermediate router’s address, it can send packets to the
destination node.
If the sending node is a router rather than a workstation, the node’s
internal routing tables supply the destination’s network location. The
destination router does not need to broadcast a RIP request.
Router’s Responsibility
A router handles a received IPX packet in one of two ways:
■
If the packet is destined for a network number to which the router is
directly connected, the sending router:
■
Places the destination node address from the IPX header in the
destination address field of the packet’s MAC header
■
Places its own node address in the source address field of the
packet’s MAC header
■
Increases the transport control field of the IPX header by 1 and
transmits the packet on the destination node segment
■
If the packet is destined for a network number to which the router is
not directly connected, the router sends the packet to the next router
along the path to the destination node. The sending router:
■
Looks up the node address in the routing information table of the
next router and places the address in the destination address field
of the packet’s MAC header