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Introduction
Page 27-2
IPX Routing Overview
In IPX routing, the switch builds routing tables to keep track of optimal destinations for traf-
fic it receives that is destined for remote IPX networks. The switch sends and receives rout-
ing messages, or advertisements, to/from other routers in the network. When the switch
receives an IPX packet, it looks up the destination network number in its routing table. If the
network is directly connected to the switch, the switch also checks the destination node
address. The network number consists of eight hex digits, and the node address is typically
the
MAC
address of the end station or server.
Creating routing tables is performed by switch software unless a Hardware Routing Engine
(HRE) or HRE-X is installed. The HRE or HRE-X significantly improves routing performance.
See Chapter 1, “Omni Switch/Router Chassis and Power Supplies,” for information about the
HRE-X respectively.
IPX is associated with additional protocols built into the switch software. These are described
in the next section.
IPX Protocols
The switch supports the following IPX protocols:
•
SPX
(Sequenced Packet Exchange) is a Transport-layer protocol that provides a reliable
end-to-end communications link by managing packet sequencing and delivery. SPX does
not play a direct role in IPX routing; it simply guarantees the delivery of routed packets.
•
IPX RIP
(Routing Information Protocol) is a layer 3 protocol used by NetWare routers to
exchange IPX routing information. IPX RIP functions similarly to IP RIP. IPX RIP uses two
metrics to calculate the best route: hop count and ticks. An IPX router periodically trans-
mits packets containing the information currently in its own routing table to neighboring
IPX RIP routers in order to advertise the best route to an IPX destination.
•
SAP
(Service Advertising Protocol) is a layer 3 protocol used by NetWare routers to
exchange IPX routing information. SAP is similar in concept to IPX RIP. Just as RIP enables
NetWare routers to exchange information about routes, SAP enables NetWare devices to
exchange information about available network services. NetWare workstations use SAP to
obtain the network addresses of NetWare servers. IPX routers use SAP to gather service
information and then share it with other IPX routers.