3Com 2500 manual Router’s Responsibility

How IPX Routing Works 6-7

To find this router, the sending node broadcasts a RIP packet requesting the best route to the destination node’s network number. The router residing on the sending node’s segment with 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. If the sending node is a router rather than a workstation, the router can get this information from its internal routing tables and need not send a RIP request.

Once the sending node knows the router’s node address, it can send packets to the destination node.

Router’s Responsibility

When a router receives an IPX packet, it handles the packet in one of two ways:

■If the packet is destined for a network number to which the router is directly connected, the router performs the following tasks:

■Places the destination node address from the IPX header in the destination address field of the MAC header.

■Places its own node address in the source address field of the MAC header.

■Increments the Transport Control field of the IPX header 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 as follows:

■The 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. For more information on routing tables, see the next section.

■The router places its own node address in the source address field of the packet’s MAC header.

■The router increments the Transport Control field in the IPX header and sends the packet to the next router.