M ost network administrators have at some point encountered IPX for two reasons first Novell NetWare uses IPX as its default protocol second it was the most popular network operating system during the late 1980s and early 1990s As a result millions of IPX networks have been installed But Novell is changing things with the release of NetWare 5 TCP IP is now the default communications protocol instead of IPX although Novell still supports IPX Why do they still bother Well considering the multitude of installed IPX clients and servers it would be pretty impractical to yank the support for it There s little doubt that IPX will be around for a while so it s no surprise that the Cisco IOS provides full support for large IPX internetworks But to really take advantage of Novell IPX s functions and features we need to review the way it operates and handles addressing because it varies significantly from the TCP IP method we covered earlier Armed with a solid grasp of things IPX we ll then explore the configuration of IPX in the Cisco IOS and from there cover the monitoring of IPX traffic Introduction to Novell IPX N ovell IPX Internetwork Packet Exchange has been in use since its release in the early 1980s It s quite similar to XNS Xerox Network Systems which was developed by Xerox at its Palo Alto Research Center in the 1960s it even shares a likeness with TCP IP IPX is really a family of protocols that coexist and interact to empower sound network communications Copyright 2000 SYBEX Inc Alameda CA www sybex com Introduction to Novell IPX 387 Novell IPX Protocol Stack IPX doesn t map directly to the OSI model but its protocols do function in layers Back when they designed IPX engineers were more concerned with performance than they were with strict compliance to existing standards or models Even so comparisons can be made Figure 8 1 illustrates the IPX protocols layers and functions relative to those of the OSI model FIGURE 8 1 IPX protocol stack and the OSI model OSI Reference Model Novell NetWare Protocols 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link IPX Internetwork Packet Exchange 1 Physical Media Access Protocols Ethernet Token Ring WAN others RIP NLSP SAP NCP NETBIOS Applications SPX IPX IPX performs functions at layers 3 and 4 of the OSI model It controls the assignment of IPX addresses software addressing on individual nodes governs packet delivery across internetworks and makes routing decisions based on information provided by the routing protocols RIP or NLSP IPX is a connectionless protocol similar to TCP IP s UDP so it doesn t require any acknowledgment that packets were received from the destination node To communicate with the upper layer protocols IPX uses sockets These are similar to TCP IP ports in that they re used to address multiple independent applications running on the same machine Copyright 2000 SYBEX Inc Alameda CA www sybex com 388 Chapter 8 Configuring Novell IPX SPX SPX Sequenced Packet Exchange adds connection oriented communications to the otherwise connectionless IPX Through it upper layer protocols can ensure data delivery between source and destination nodes SPX works by creating virtual circuits or connections between machines with each connection having a specific connection ID included in the SPX header RIP RIP Routing Information Protocol is a distance vector routing protocol used to discover IPX routes through internetworks It employs ticks 1 18 of a second and hop counts number of routers between nodes as metrics for determining preferred routes SAP SAP Service Advertising Protocol is used to advertise and request services Servers use it to advertise the services they offer and clients use it to locate network services NLSP NLSP NetWare Link Services Protocol is an advanced link state routing protocol developed by Novell It s intended to replace both RIP and SAP NCP NCP NetWare Core Protocol provides clients with access to server resources functions such as file access printing synchronization and security are all handled by NCP What does the presence of routing protocols connection and connectionless transport protocols and application protocols indicate to you All of these factors add up to the fact that IPX is capable of supporting large internetworks running many applications Understanding how Novell uses these protocols clears the way for you to include third party devices such as Cisco routers into an IPX network Client Server Communication Novell NetWare follows a strict client server model there s no overlap a NetWare node is either a client or a server and that is that You won t find peer machines that both provide and consume network resources here Clients can be workstations running MacOS DOS MS Windows Windows Copyright 2000 SYBEX Inc Alameda CA www sybex com Introduction to Novell IPX 389 NT OS 2 Unix or VMS Servers generally run Novell NetWare NetWare servers provide the following services to clients File Print Message Application Database As you would think NetWare clients need servers to locate all network resources Every NetWare server builds an SAP table comprised of all the network resources that it s aware of We ll explain how they do this a bit later in the chapter When clients require access to a certain resource they issue an IPX broadcast called a GNS GetNearestServer request so they can locate a NetWare server that provides the particular resource the client needs In turn the servers receiving the GNS check their SAP tables to locate a NetWare server that matches the specific request they respond to the client with a GNS reply The GNS reply points the client to a specific server to contact for the resource it requested If none of the servers receiving the client s GNS request have or know of another server that has the requested service they simply don t respond which leaves the requesting client without the ability to access the requested resource Why do we care Because Cisco routers build SAP tables too and because they can respond to client GNS requests just as if they were NetWare servers This doesn t mean they offer the services that NetWare servers do just that their replies are identical when it comes to locating services The GNS reply to a client can come from a local NetWare server a remote NetWare server or a Cisco router and generally if there are local NetWare servers present they should respond to the client s request If there are no local NetWare servers however the local Cisco