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IPX Routing Basics on NetWare Servers
Formerly KB 2932631
Sending Node's Responsibility:
When a node wants to send information to another node with the same network number, the sending node can simply address and send packets directly to the destination node. However, if the two nodes have different network numbers, 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, a workstation broadcasts a RIP packet requesting the fastest route to the destination node's network number. The router residing on the sending nodes segment with the shortest path to the desired segment responds to the RIP request.
Once the sending node knows the router's node address, it is prepared to send packets to the destination node. The sending node addresses these packets in the following way:
1. Places the destination node's internetwork address (network, node, and socket number) in the destination address field to the IPX header.
2. Places its own internetwork address in the source address field of the IPX header. (All other fields in the IPX header must be filled out as well.)
3. Places the node address of the router (the one that responded to the RIP request if the sending node is a workstation) in the destination address field of the MAC header.
4. Places its own node address in the source address field of the MAC header and sends the packet.
When a router receives an IPX packet, its IPX handling process should do the following:
1. Check the IPX header Transport Control Field (hop count). If this field is equal to or greater than 16 the packet should be discarded.
2. Check the IPX header Packet Type field. If the Packet Type is 20, the router acts according to what NetBIOS propagation level is set.
3. Check the IPX header Destination Address field (network, node, and socket) to determine how to route the packet. If the packet is addressed to the router it should be handled internally by the appropriate socket process, otherwise further routing will be required as described next.
When forwarding packets, the router can take one of two possible actions. If the packet is destined for a network number that the router is directly connected to, the router performs the following steps:
1. Places the destination node address from the IPX header in the destination address field of the MAC header.
2. Places its own node address in the source address field of the MAC header.
3. Increments the Transport Control field of the IPX header (hop count), and transmits the packet onto the destination node's segment.
Note that each frame bound to a router's LAN adapter is treated as a separate, logical segment, each segment with its own distinct network address. This information is stored in the router's RIP table and on that basis the router forwards the packets just the same as to a physical segment.
If, however, the router is not directly connected to the segment that the final destination node resides on, it will send the packet to the next router in the path to the destination node. To forward to another router:
1. The router places the node address of the next router in the destination address field of the MAC header.
2. It places its own node address in the source address of the MAC header.
3. It increments the Transport Control field in the IPX header (hop count) and sends the pack to the next router.
Note that in the two cases just described, under normal conditions the only modification that the router makes to the IPX header when routing a packet is incrementing the Transport Control field (hop count). All other fields are left as initially set by the sending node. Of course if the router is generating one of its own packets it will need to fill in the entire IPX header and perform the functions of a sending node.
Keywords: NetWare intraNetWare 4.10 4.11 route router routing ipx/spx LAN WAN