Routing & Switching

How to set up a terminal server on GNS3.

Sometimes, when the network topology involves many routers, managing all of them becomes a little bit annoying due to the huge number of windows terminals opened. Luckily, exists the terminal servers, that is, routers acting as a gateway between us and the rest of the routers. With a terminal server, we only have one terminal window opened but we still being able to reach any other router.

Traditional routers used for remote console access are the Cisco 2500 Series, they are the typical choice for people building their home labs. They come together with an octal cable or independent null cables, depending the model:

Of course this is configurable on GNS3. To do that, we need to have a loopback interface previously configured in the operative system. This task is very straight forward and I will not cover it in this post, but you can follow this link if you are a Windows 7 user or this one for XP.

Once the virtual adapter is present, you assign an ip address, in this example I’ll use the 172.31.255.254/30. This mask allows for enough addresses.

Next step is to add a cloud in GNS3 and bind it to the loopback interface:

 

Following, add a new router to the topology, connect one of the FastEthernet interfaces to the Cloud and assign the remaining ip 172.16.31.255.253/30. Check connectivity between them:

TS(config)#do ping 172.31.255.254
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.31.255.254, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/23/40 ms

Collect the console ports numbers for each router and configure the corresponding ip hosts in the terminal server device:

TS(config)#ip host R5 2004 172.31.255.254
TS(config)#ip host R1 2000 172.31.255.254
TS(config)#ip host R4 2003 172.31.255.254
TS(config)#ip host R7 2006 172.31.255.254
TS(config)#ip host R6 2005 172.31.255.254
TS(config)#ip host R3 2002 172.31.255.254
TS(config)#ip host R2 2001 172.31.255.254
TS(config)#ip host R8 2007 172.31.255.254
TS(config)#ip host R9 2008 172.31.255.254
TS(config)#ip host R10 2009 172.31.255.254

And we’ve made all the necessary configuration. Now check access:

TS#r5
Translating "r5"
Trying R5 (172.31.255.254, 2004)... Open
Connected to Dynamips VM "R5" (ID 8, type c3725) - Console port
Press ENTER to get the prompt.
R5#

Go back to the TS is as simpler as pressing the keystroke Crtl-Shift-6 + x. Once you are on the TS, pressing return will reconnect automatically to the last router.

To review which connections we have opened, use the command sh sessions:

TS#sh session
Conn Host                Address             Byte  Idle Conn Name
   1 r5                  172.31.255.254         0    46 r5
   2 r1                  172.31.255.254         0    45 r1
   3 r7                  172.31.255.254         0     3 r7
*  4 r5                  172.31.255.254         0     0

For resume a session just press the connection number. From the table above, pressing 3 will resume the connection to R7:

TS#3
[Resuming connection 3 to r7 ... ]
R7(config)#

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