NOTE This section is included to place EIGRP in context. The exam will test only on topics pertaining to EIGRP using IP. Therefore, this section should be read only for interest and should not be studied in depth in preparation for the Routing exam.
The configuration of IPX is very similar to IP. The difference is that IPX is a client/server-based protocol that was originally designed to operate in a LAN environment. Although Novell has improved its technology over the past few years to allow the networks to scale across the enterprise domain, IPX can still prove both a design and an implementation headache for the administrator. Typically, the amount of overhead generated in a client/server network is greater than that of a peer-to-peer network. This overhead becomes problematic when slower WAN links are used and bandwidth is at a premium. In this environment, EIGRP is a powerful tool.
EIGRP offers the following main features to an IPX enterprise network:
• Incremental updates for both RIP and SAP traffic
• Faster convergence of the network
• An increased diameter of the network, through the use of the metric and hop count
• A more complex and sophisticated routing metric
• Automatic redistribution of networks among IPX RIP, NLSP, and EIGRP
The operation of EIGRP for IPX is the same as that of IP, although the EIGRP metric uses both bandwidth and delay in calculating the best path.
EIGRP for IPX uses the same major components:
• Reliable transport mechanism for updates
• Neighbor discovery/recovery
• Protocol-dependent modules
It is important to remember that IPX is still designed as a proprietary LAN client/server protocol. EIGRP is also a proprietary protocol, and although there are some devices on the market that support EIGRP, it cannot be assumed that these include IPX systems. In the design of the network using EIGRP, IPX RIP/SAP or NLSP will be running. These protocols are found on the LAN in the traditional client/server domain.
In the design of IPX in an enterprise network, EIGRP is used between Cisco routers when bandwidth is a precious commodity. Therefore, EIGRP is configured in the WAN, where it is unlikely that there are any clients or servers requiring RIP/SAP updates.
When IPX is configured on a Cisco router, it is necessary to turn on IPX routing and to allocate network addresses to the appropriate interfaces. This allows the router to route IPX traffic through those interfaces and to send and receive RIP/SAP updates.
Configuring EIGRP for IPX requires some additional commands. An additional routing protocol must be identified along with the interfaces that it supports. These interfaces are then removed from the RIP/SAP update schedule.
Example 7-1 is a sample configuration of a network that has both RIP/SAP and EIGRP running.
Router(config)# ipx routing Router(config)# ipx router eigrp 100 Router(config-router)# network FADED Router(config)# ipx router rip Router(config-router)#no network FADED Router(config)#interface E0 Router(config-if)#ipx network FAB Router(config)#interface E1 Router(config-if)#ipx network CAB Router(config)#interface E2 Router(config-if)#ipx network DAB Router(config)#interface s0 Router(config-if)#ipx network FADED
NOTE The autonomous system number used in the configuration of EIGRP for IPX must be the same on every router that wants to share routing updates. This is the same as the configuration for IP. The IPX autonomous system number is completely independent of the IP autonomous system number.
It is important to remember to remove the network command in IPX RIP routing configuration, as shown in the previous example. Otherwise, the system will continue sending IPX RIP updates in addition to IPX EIGRP updates, thus further affecting performance in the serial link.
EIGRP will automatically redistribute its routing information into RIP/SAP. It will also send only incremental updates through serial interfaces and will send periodic updates through LAN interfaces. EIGRP can be manually configured to send incremental updates out of the LAN interface, if required. Incremental updates might apply to networks that form a backbone in the network design—for example, where an FDDI ring or Fast Ethernet segments are connecting the distribution layer and forming the campus backbone.
The following is the command syntax to force a LAN interface to send incremental updates: interface f0
ipx sap-incremental eigrp autonomous-system-number
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