IPX 101

Note: This is a very brief introduction to IPX networking. For more in depth information, there are a number of excellent references. In particular, Rick Sant'Angelo's "NetWare Unleashed" (SAMS Publishing) provides a good overview of IPX routing along with tips on getting IPX drivers correctly loaded on client machines.

IPX Routing Basics

All routable protocols work by dividing the physical devices on a network into logical groups. A logical group will typically consist of all of the machines on a physical network segment (such as an Ethernet segment).

Each group of devices is assigned a unique "network number" which represents that particular group to all of the routers on the network. Packets which are sent between members of the same group are simply sent directly from one member to another. Packets which must go between devices belonging to two different groups travel through routers, which forward them along an optimal path.

By examining the destination network number in a packet that must be forwarded, and by using information that routers automatically pass between themselves in IPX Routing Information Protocol (RIP) packets, any router can determine the optimal path for forwarding packets from one group to another.

This scheme relies on the fact that each segment is assigned a unique network number. If not, the routers have no way of knowing which of the physical segments with that number should actually receive a packet.

Among routable network protocols, IPX is relatively simple. Each physical network segment is assigned a network number by the routers on the segment. The network number can be in the range of 1 to FFFFFFFE (that's 8 hexadecimal digits).

Establishing the network number for an IPX network segment is referred to as "seeding" the network. You should generally only have one seed router per network cable segment. It may sometimes be desirable for redundancy to have several seed routers on a segment. This is acceptable as long as all seed routers on the segment are seeding the same network number.

Service Advertising Protocol

Routers participate in allowing end nodes to access IPX services (such as file servers, print servers, communications servers, etc.) by keeping a list of all of the services on an IPX internetwork. This list is maintained by examining the Service Advertising Protocol (SAP) packets which are sent by servers and other routers on the local segment, and by rebroadcasting this information out of their other ports.

A "split-horizon" technique is used so that routers do not duplicate information which is already known on the segment being broadcast to.

Client Machine Addressing

Unlike TCP/IP, IPX workstations do not have fixed network/node addresses that need to be configured. Instead, a workstation gets its network number from the router(s) on the segment it is connected to, and uses its Ethernet address for its node number. This means that an IPX workstation may have as much as 18 hexadecimal digits of network/node address. Fortunately for workstation users, the Netware client software does the work of discovering the network number and setting the address. Users only need to install Novell drivers to be able to use the IPX protocols over their network.

Note: As explained below, to communicate using IPX, CompatiView requires that ODI drivers be installed on the machine it is running on. However, other than the CompatiView machine, Novell client machines can use earlier versions of Novell's drivers to communicate through Compatible Systems routers.

Routers which support IPX can use any of four "frame types" to send IPX packets. Each frame type organizes the IPX information in a network packet (i.e. frame) in slightly different fashion. Although the basic information may be the same, clients or servers using different frame types cannot communicate with each other without an intermediate translation occurring between frame types. This translation is called "transitional routing," and is one of the functions that can be performed by routers.

The four IPX frame types are:

• Ethernet_Type_II
• Ethernet_802.3 (Raw)
• Ethernet_802.2
• Ethernet_SNAP

Older versions of NetWare defaulted to the 802.3 Raw frame type, whereas NetWare 4.0 uses the 802.2 frame type.

For this reason, the default configuration for Compatible Systems routers which support IPX has both 802.3 Raw and 802.2 set to autoseed (they will come up regardless of whether there is a server on line or not) and the other two frame types set to non-seed (they won't come up unless they "hear" another router using this frame type.

This autoseeding default router configuration simplifies administration of the router since IPX can be routed right out of the box without any configuration. To determine a network number to use for autoseeding, a router listens to the network for several RIP periods, and then examines its routing table (which is filled in with information from RIP packets), and picks an unused number.

Tips On Installing IPX/ODI Drivers

Instructions for installing the IPX/ODI software on your PC are contained in the Novell Netware ODI Shell for DOS manual. These instructions are for workstations running DOS and Windows. If you are running Windows for Workgroups see the section later in this appendix since these instructions will not apply.

For DOS you need to do the following things (some or all of which you may have already done if you are using Netware today):

1. Copy Ethernet drivers for your network card to the boot disk.
2. Modify your autoexec.bat file to load IPXODI at boot time.
3. Create/Modify a NET.CFG file (if necessary).

Some PC Ethernet card vendors include driver diskettes with their products. Run their installation program and install the ODI driver for your card. If they have not included drivers, look in the DOS/ODI directory of the DOS ODI WORKSTATION SERVICES diskette for the driver. You may also want to check with the card vendor, and with CompuServe or other online services.

Typically, your autoexec.bat file will need to contain the following lines to get IPXODI loaded correctly. The example is for a NE2000 card and loads the IPX shell with NETX.

• LSL
• NE2000
• IPXODI
• NETX

If you have not changed the default hardware settings on your Ethernet card then the NET.CFG file may not be necessary. It is required if the settings are different or if you plan on using more than one protocol (TCP/IP for instance). An example NET.CFG file is given below. This example has support for both IPX and TCP/IP.

• LINK SUPPORT
• BUFFERS 16 1600
• MEMPOOL 24K
• LINK DRIVER NE2000
• INT 5
• MEM C8000
• FRAME ETHERNET_802.3
• FRAME ETHERNET_II
• PROTOCOL IPX 0 ETHERNET_802.3
• PROTOCOL IP 800 ETHERNET_II
• PROTOCOL ARP 806 ETHERNET_II
• PROTOCOL RARP 8035 ETHERNET_II

Windows for Workgroups is capable of being configured to provide IPX services to applications programs in a similar way to ODI. Normally, you can specify IPX/SPX as an option when you install Windows for Workgroups. However, if it wasn't installed you can add it using the Network Setup application. Follow the steps given below:

1. Open the Network Setup application.
2. At the Network Setup screen click on the Drivers button.
3. At the Drivers screen click on the Add Protocol button.
4. At the Add Network Protocol screen choose one of the IPX/SPX Compatible Transport items and click OK. The new protocol will be added below the card name in the Network Drivers list box.
5. Select this new item and click on the Setup button.
6. Choose Frame Type in the Advanced Protocol Settings list box. Then choose the frame type you want to use from the popup below.

The IPX drivers have now been installed and you will need to exit and restart Windows for your changes to take effect.