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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.
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