AIS AI2524 user manual Configure X.25 Routing

Chapter 12: AI2524 X.25 Configuration Steps

Configure X.25 Routing

The X.25 software implementation allows virtual circuits to be routed from one X.25 interface to another and from one router to another. The routing behavior can be controlled with switching and X.25-over-TCP (XOT) configuration commands, based on a locally built table.

X.25 encapsulation can share an X.25 serial interface with the X.25 switching support. Switching or forwarding of X.25 virtual circuits can be completed two ways:

zIncoming calls received from a local serial interface running X.25 can be forwarded to another local serial interface running X.25. This is known as local X.25 switching because the router handles the complete path. It does not matter whether the interfaces are configured as DTE or DCE device because the software takes the appropriate actions.

zAn incoming call also can be forwarded to another Cisco router over a LAN using the TCP/IP protocols. Upon receipt of an in- coming call, a TCP connection is established to the router that is acting as the switch for the destination. All X.25 packets are sent and received over this reliable data stream. Flow control is main- tained end-to-end. This is known as X.25-over-TCP or XOT. (XOT was previously called remote switching or tunneling.) It does not matter whether the interfaces are configured as DTE or DCE, because the software takes the appropriate actions.

Running X.25 over TCP/IP provides a number of benefits. The data- gram containing the X.25 packet can be switched by other routers using their high-speed switching abilities. X.25 connections can be sent over networks running only the TCP/IP protocols. The TCP/IP protocol suite runs over many different networking technologies, in- cluding Ethernet, Token Ring, T1 serial, and FDDI. Thus X.25 data can be forwarded over these media to another router where it can b output to an X.25 interface.

When the connection is made locally, the switching configuration is used; when the connection is across a LAN, the XOT configuration is used. The basic function is the same for both types of connections, but different configuration commands are required for each type of con- nection.

August 1997	Page 12-29
2524UM