This chapter discusses the Compatibility Mode Driver, and using it to support IPX in a NetWare 5.1 network. The objectives important to this chapter are on page 9-1:
Concepts:Configure the Compatibility Mode Driver (CMD)The chapter begins with a discussion about IPX. The IPX protocol suite was unique to Novell networks. Before the advent of NetWare 5, IPX was required. Now, Novell recommends that you not use IPX. This is not always possible. You may have legacy applications that require IPX to work. You may not have the time or money to convert an entire existing Novell network to NetWare 5 or 5.1 at once. While it is possible to support both the IP and IPX suites on your network, Novell warns that this takes a lot of bandwidth, and it makes the eventual migration away from IPX more difficult later on. Novell recommends installing IP only, but also installing the Compatibility Mode Driver (CMD), which makes it possible to run IPX applications. The CMD has two components that must both be installed: one for the server, and one for the client. The server component of the CMD is SCMD.NLM, which is loaded automatically from AUTOEXEC.NCF on NetWare 5.1 servers that use IP but do not use IPX. The driver works like this:
This approach may be thought of as the opposite of using NetWare/IP. Using this older approach, the actual protocol used on the network was IPX, but packets could be encapsulated in IP envelopes to pass them across a WAN that did not support IPX. On a workstation, the CMD is loaded so the workstation can use IPX-based services on an IP-only network. This means that the workstation does not send IPX packets. Remember, our goal here is to eliminate IPX traffic on the network. If your network has IPX servers on it, the CMD will allow the workstation to communicate with those servers as well by passing requests to an IP-based server that acts as a go-between. The go-between is referred to as a Migration Agent. Tasks performed by the CMD on a workstation:
To load the Compatibility Mode Driver on a server, place the command LOAD SCMD in the AUTOEXEC.NCF file. It should go after the command to bind IP to the NIC. SCMD will automatically load an IPX stack, if not already loaded. SCMD will fail to load if an IPX stack is bound to the NIC. Novell recommends loading IPXRTR.NLM (an IPX router) when you load SCMD. When CMD is loaded, it creates a virtual IPX network on your network. It is assigned a Network number by default: FFFFFFFD. To create a virtual IPX network with a different number, use the command LOAD SCMD /NET=IPX_Network_Number Every device on your network must use the same virtual IPX network, so Novell recommends that you use the default number, unless you have a good reason to configure each device to use another number. Methods for loading the CMD on a workstation:
Once CMD is loaded on a workstation, it must be configured. You can configure your DHCP server to supply configuration data to workstations, or you can configure them individually. Both options allow you to specify the address for a virtual IPX network. Configure CMD to Provide Migration Agent and Backbone SupportThe Compatibility Mode Driver has the capacity to perform two other major tasks: acting as a Migration Agent and providing Backbone Support to your network. A Migration Agent is a service, provided by the CMD, that "speaks" both IP and IPX. A Migration Agent translates traffic between sections of the network that only use one of these protocol suites. In this sense, the Migration Agent performs gateway services on the network. The Migration Agent is needed when you have two parts to your network. You may, for example, not have funding to migrate all servers in an existing IPX network to IP at one time. The IP segment of the network works as described above:
If a client on the IPX segment needs IP-based services:
The next part is tricky. If you actually have two network segments, you will have two NICs in the server providing MA service: one for the IP net and one for the IPX net. Obviously, you must bind IPX to the NIC that connects to the IPX net. If you only have one network segment, but it contains IPX servers and clients as well as IP servers and clients, you will have to load and bind IPX to the same NIC that you bind IP to on the MA server. This violates the rule stated above about NOT binding IPX on a server running the CMD. You avoid the problem by first loading and binding IPX, then loading the CMD with this command: LOAD SCMD /MA Migration Agents are found on a network, by default, using multicast requests. To avoid this, you can configure the other servers on the network to use unicasts to a specific address. Use the following command before loading SCMD.NLM on those servers. SET PREFERRED MIGRATION AGENT LIST:MA_IP_address/ You may establish a list of MAs by using multiple IP addresses, separated by semicolons. The list must end with a forward slash, like the example above. CMD client software may be configured to discover MAs dynamically or it may be configured to use a list of IP addresses. The two modes are not compatible, so you should choose one or the other. DHCP service can provide either option to the client software, as can hand coding the configuration on each workstation. The other feature of the CMD software is backbone support, also called IP tunneling. IPX packets can be encapsulated in IP packets, passed across an IP network, and then delivered to a different IPX network. This works, as above, when the MA is configured on servers that act as routers between IP and IPX networks. It also works when using dedicated hardware routers that do not run NetWare. The scenario is the same, except that the servers pass the encapsulated packets to actual routers, instead of passing them directly to the next network/segment. Identify IPX to IP Migration Strategies
Novell recommends that an existing IPX network be migrated to IP-only as soon as you can do so. Three scenarios are presented for doing so:
The "section at a time" approach can be done in a number of ways. Three methods are discussed in the chapter. You should review each of them.
|