2.2 Configuration for Asynchronous Connections
2.2.1 Connecting to the modem

Generally, access servers support both incoming asynchronous line connections (forward connections) and outgoing asynchronous line connections (reverse connections), as shown in Figure . For example, a remote terminal user who dials into the access server through an asynchronous line makes a forward connection; a user connects through an access server (reverse connection) to an attached modem to configure the modem. This reverse connection is referred to as reverse Telnet.

A host can make reverse Telnet connections to various types of devices attached to an access server. Different port numbers (20xx, 40xx, and 60xx) are used because different data type and protocol negotiations will take place for different types of devices attached to the access server.

The remote host must specify a particular TCP port on the router to connect with individual lines or to a rotary group. For example, in Figure , if you wish to configure a modem connected to the interface Async 7, you will make a reverse Telnet connection using port address 2007. Note that TCP port number 2007 specifies a Telnet protocol connection (TCP port 2000) to line 7. The individual line number is added to the end of the port number type.