How to Configure a Terminal Server

Terminal Server Overview
A terminal server provides out-of-band access for several devices.
Out-of-band access is through a router's console or aux port versus in-band access that occurs over the network using telnet or ssh.
Generally, a terminal server is a router with multiple, asynchronous ports that are connected to other devices,
such as the console port of other routers or switches.

Terminal Server Configuration (Telnet)
Steps 1: Creating a Loopback Interface and Assigning an IP Address
int f0/0
ip add 192.168.1.1 255.255.255.255
Step 2: Allowing Telnet as a Transport Across Asynchronous Lines 0/0/0 0/0/7
line 0/0/0 0/0/7
transport input telnet
Step 3:
conf t
ip host R1 2002 192.168.1.1 !R1 is connected to port 2 on the Terminal Server. The ip host command is a static DNS entry used by the router.
ip host R2 2003 192.168.1.1 !The port number is 2000 + line number.
ip host R3 2004 192.168.1.1
ip host R4 2005 192.168.1.1
end
wr


Terminal Server Configuration (SSH)
Step 1: Creating a Loopback Interface and Assigning an IP Address
int f0/0
ip add 192.168.1.1 255.255.255.255

Step 2: For SSH access, the tty lines do not listen to the same ports as telnet does. So you need to define the ports manually with the use of the rotary group.
Configure SSH to listen to a range of ports and map them to rotary group.
conf t
ip ssh port 2001 rotary 1 127
!
line 0/0/0
login local
rotary 1
no exec
transport input ssh
line 0/0/1
login local
rotary 2
no exec
transport input ssh
line 0/0/8
login local
rotary 11
no exec
transport input ssh
line 0/0/9
login local
rotary 12
no exec
transport input ssh
end
wr
Step 3. Configure your vty lines for SSH as outgoing protocol. Since you open reverse connections to the lines, it comes from vty line and hence SSH should be allowed.
line vty 0 4
transport output ssh
login local
Step 4: Ensure that you have configured the usernames correctly based on the authentication criteria that is used. In this configuration example, you have configured a local username cisco with password cisco.


Connecting
1. From ther terminal server, telnet 192.168.1.1 2002 or ssh -l cisco -p 2002 192.168.1.1
2. From laptop that has network connection to the terminal server, ssh -l cisco:2 192.168.1.1. - cisco:2 (where 2 is the line number)
3. From termanal server, type the hostname. For example, R1.
4. Enter the session (conn) number to connect to the corresponding device.
5. Use Terminal Application - With the use of SSH client software, you can connect through SSH with the use of the port based on the mapping on terminal lines.
6. Access Devices through Menu Options.

Disconnecting
1. Ctrl-Shift-6 then x to exit the current session or return to the terminal server. This does not kill the connection but puts it in the background.
2. clear line 1 !When the connection is refused, you need to clear the asynchronous line and attempt the reverse Telnet again.
3. disconnect [conn number next to *] from show session command.

Verifying Reverse Telnet/SSH Sessions
1. show sessions command to display all open connections.
2. show host to verify host ip mapping
3. show line
4. show users


Troubleshooting Notes
You might have observed that sometimes the connection is refused by remote host when you connect, to resolve this disconnect
any active connection from menu option or from cli exec mode use the command clear line [line number] and try to connect to the device again.


References:
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[ Ссылка ] - Configuring Cisco Access Server Packet Tracer - Pinoy
[ Ссылка ] - Terminal Server Configuration in Packet Tracer no sound

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