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View Full Version : CTRL+SHIFT+6 X - Cisco Reverse Telnet


Smooth
01-15-2007, 08:51 AM
Hi, I have made a standard telnet connection to a remote Cisco 2511 router - that works fine. That 2511 acts as a Terminal server using an Octoal Cable to 16 other rotuers. When I connect to each router, I am not able to reverse out using Ctrl+shift+6 X. I have tried this several times, and used different keyboards to eliminate hardware malfunction. Do you have any ideas as to why I cant break out?. All that happens is my session hangs and I have to re-connect.

Version 4.0.3 (Build 401) is what I am using.

tnygren
01-15-2007, 01:41 PM
Hi Smooth,

I'm sorry to hear that 'Ctrl' + 'Shift' + '6' + 'x' is not working to return you to the main console.

I just need to get a little more information to find out what is happening.

Has this just started to happen?

If the latest version of CRT/SecureCRT (5.2.1) is used, does the issue still happen?

Are other telnet clients (such as the built in Windows telnet client) also having this issue?

Smooth
01-16-2007, 03:15 AM
Has this just started to happen?

Well, I have just started to use this - so no, it's not sudden I guess.


Are other telnet clients (such as the built in Windows telnet client) also having this issue?

I just tried HyperTerm and the same thing happens. [/QUOTE]

If the latest version of CRT/SecureCRT (5.2.1) is used, does the issue still happen?

Yes, I have tried an alternate version, the latest one - same issue. Hmm, I wonder then, if I need something on my router. So bizarre, when I console in it's fine with any verison, when I telnet in - that's when it happens. So I need something on my line vty 0 4 to accept that combination of key strokes. Any one have any ideas?

tnygren
01-16-2007, 08:25 AM
Hi Smooth,

It does appear that there is something on the router that is not correctly using reverse telnet to go to back to the main console.

I am not familiar with the Cisco 2511 router setup to help with what needs to be changed.

We do have other forum users that have mentioned that they use this router and may be able to help. You also might want to post to Cisco's forums to see if they might have some ideas also.

Smooth
01-16-2007, 08:38 AM
Hi,

Thanks very much, I appreciate now that is this is a Cisco IOS issue, I will post over there now.

:)

tnygren
01-16-2007, 09:55 AM
Hi Smooth,

You are very welcome! :)

Please let us know if there are any other questions on any of our products.

mekanik
01-16-2007, 10:59 AM
Hi,

Thanks very much, I appreciate now that is this is a Cisco IOS issue, I will post over there now.

:)

Are you TELNET'ng directly to the 2xxx port of the 2500 (direct reverse TELNET connection), or are you TELNET'ng into the 2500 and then connecting from IOS to the device, thus 2-hop method?

It sounds as though you are directly TELNET'ng to the 2xxx port of the 2500, and if this is the case, then 'Ctrl' + 'Shift' + '6' + 'x' won't work at all. You'll need to first connect to the 2500 and then perform your reverse-telnet from the IOS device and then use 'Ctrl' + 'Shift' + '6' + 'x' to escape back to the 2500 and then use "show session" and "resume" to switch between and manage the reverse-console sessions. If you are doing a direct TELNET from a unix/linux based system to the 2500 on the 2xxx port, then you can use the TELNET escape of "Ctrl" + "]" and then enter "z" at the "telnet>" prompt and you can manage you session using the "jobs" and "fg %<job-number>".

'Ctrl' + 'Shift' + '6' + 'x' has never been been a problem for me when using SecureCRT and Cisco IOS devices...

--
mekanik

Smooth
01-16-2007, 11:48 AM
Hi, Yes it's the 2 hop method, that is where the problem is. I am doing a telnet to the E0 port of the 2511 and then once logged on to it, doing another telnet to through the break-out cable. The cliend I am using is Windows XP. The problem is the 2 hop's I think.

Grunt11B
01-19-2007, 06:34 AM
The reason this happens is the first router interprets the key combination as a local command. Instead of of using this router as a hop, reverse telnetting into the serially attached devices using the available VTYs will pass the key combination through the terminal router and the attached routers will interpret the keys instead.

IIRC: Telnet to the IP of the terminal server, but use "20xx". "xx" being the port the destination router is attached to. For instance, telnet to 1.1.1.1 using port 2010 to connect to the device on serial port 10. It's been serveral years since I've worked reverse telnet, so expect to do some research to verify your config.

Smooth
01-21-2007, 07:43 AM
Hi Christopher,

Thanks for you advice. After further investigation I have found out what the problem is. Now, when I telnet to the E0 port of the TServer I am able to issue the key combination with no problems providing I do not use a specific IP address. What I mean is, I got some friends to telnet over the internet using their DSL and cable connection, and it worked - the CTRL+SHIFT+6 X. When I telnet to the router form my work IP address (that is behind a proxy) it does not work.

When I issue a sh users on the 2509 I see the IP address and hostname of the DSL/Cable users, and I can ping back to them. When I do that the same for the proxied address I see only the IP address and I am NOT able to ping it. What I am guessing is, that whatever packet the break command assembles is not routing back to the proxied address - however the telnet commands are. SO I really need to find out what the makeup of the BREAK command is and think of a way of routing it.

I was thinking of some form of reverse NAT but Im not sure yet.

Grunt11B
01-21-2007, 08:47 AM
Oh well, my wife often points out my memory deficiencies as well. :-)