Configuring IPX RIP

IPX RIP is a NetWare dynamic routing protocol similar in function to IP RIP. IPX RIP is a distance vector routing protocol that establishes and maintains IPX routing tables between IPX routers and NetWare servers. We discussed IP RIP and the properties of distance vector routing protocols in Chapter 4. IPX RIP is an interior gateway protocol (IGP). There is no exterior gateway protocol (EGP) routing protocol in IPX because NetWare runs on intranets , not over the public Internet. IPX RIP is enabled on all IPX interfaces by default when you use the global configuration command ipx routing .

IPX RIP was the first dynamic routing protocol for IPX networks, so it lacks some advanced features of newer dynamic routing protocols in terms of address and route summarization, convergence speed, route selection criteria, and scalability. As you will see later in this section, NLSP and EIGRP ”more modern dynamic routing protocols for IPX ” solve some of these issues.

While IP RIP uses hop count as its routing metric, IPX RIP uses a different metric, known as clock ticks , to make routing decisions. A clock tick represents one- eighth of a second. The clock tick metric for a destination is measured by examining the bandwidth on the interface used to reach that destination. In the output of show ipx route from the SF-2 router, the route to IPX network 100 has a metric of two clock ticks and one hop, shown as [02/01] in the IPX routing table:

 SF-2#  show ipx route  Codes:     C - Connected primary network, c - Connected secondary network S - Static, F - Floating static, L - Local (internal), W - IPXWAN R - RIP, E - EIGRP, N - NLSP, X - External, A - Aggregate s - seconds, u - uses 4 Total IPX routes. Up to 1 parallel paths and 16 hops allowed. No default route known. C         10  (NOVELL-FDDI),  Fd0 C        150 (NOVELL-ETHER),  Et1 C        200 (NOVELL-ETHER),  Et0 R 100 [02/01] via 100.0000.1c2c.23bb, 19s, Fd0 

If the number of clock ticks to reach a destination is equal for multiple routes in the IPX RIP routing table, the router uses the shortest number of router hops to break the tie. IPX RIP has a default maximum hop count of 16, just like IP RIP. Like all routed protocols in the IOS, the router load-shares the traffic to the destination through all available equal-cost paths if the routing table has equal-cost paths (if both clock ticks and router hops tie).

Note

By default, a router using the Cisco IOS does not learn about multiple IPX parallel equal-cost paths to a given destination. The router learns a single path to a destination and discards information about alternative parallel equal-cost paths, as indicated by the show ipx route phrase "Up to 1 parallel paths and 16 hops allowed." This default behavior is based on the implementation of some NetWare clients and services that cannot handle IPX packets arriving out of order ”which can happen when load sharing occurs over parallel equal-cost paths.

To enable a router to place equal-cost paths in its IPX routing table, use the global configuration command ipx maximum-paths . For example, the command ipx maximum-paths 2 allows the router to learn about two equal-cost paths for a given destination. The number of equal-cost paths you enable on your router depends on your IPX network topology.

The default behavior of a Cisco router is to load-share on a per-packet basis over all parallel equal-cost paths for a destination IPX address. For performance reasons, you may want all packets for each unique destination IPX address to take the same path even if multiple equal-cost paths exist. To enable this feature, use the IOS global configuration command ipx per-host-load-share .