Planning a Configuration to Run IP Over X.25

This section gives you an idea of how to plan a configuration to run IP over X.25, and to help you find the information you need to do so. Internetworking with TCP/IP: Principles, Protocols, and Architecture, by Douglas Comer, is a useful source of information on IP routing. The SunOS 5.0 manual Administering TCP/IP and UUCP also has information on routing that will help you to plan for your own particular system.

The following is a summary of what you need to do if you plan to use IP routing over X.25:

• Obtain and allocate IP addresses.

  Every IP network that you intend to connect with other IP networks must have a unique IP network number.

• Decide whether to use dynamic or static IP routing. You need to weigh the cost of running a dynamic routing protocol such as RIP across an X.25 connection, against the cost of network downtime caused by out-of-date static routing tables. This decision will be influenced by the size and complexity of your network, as well as by the importance of maintaining connections.

  If you decide to use dynamic routing, you need to initiate RIP, the Routing Information Protocol. This is provided in the file in.routed. The contents of the file are broadcast every 30 seconds. You can also use gated, if it is available on your system.

  A good compromise between using dynamic and static routing is to configure a static route to a routing gateway that is not attached to the X.25 network. The routing gateway can then handle the dynamic routing of traffic that does not need to cross the X.25 network.

  To look at the contents of the routing table, enter netstat --r.

• Provide address resolution information, to allow IP addresses to be translated into X.25 addresses, and vice versa. You do this using the IP Interface Configuration window and the Remote Host to X.25 Address Map window. Both windows can be accessed through the Services menu in x25tool. You do not need to provide the address resolution information if you are connecting to the DDN. The DDN uses an automatic address translation mechanism, defined in RFC 1236.