CCIE Lab » Linux

Telnet handler in Firefox-(K)Ubuntu

Radu — Wed, 04 Nov 2009 16:16:17 +0000

In labs we use reverse telnet to access our equipment (as in “routers and switches”) directly into console. To make things a little bit easier for our students we created a web page with “telnet://” links pointing directly to each router/switch.
That should be enough to solve all those pesky little questions like “what was that address again ?”. And it is. At least when the computer used by our students is running Windows. But we do have a little problem because all our computers in the lab are running Ubuntu. And Firefox. And it appears that Firefox in Ubuntu doesn’t know how to handle “telnet://” links.

I solved the problem by installing Opera browser and add the telnet handler in Opera. Or even better, install Opera and Putty and use Putty to handle “telnet://”. But the problem with Firefox kept bugging me and even if I’m lazy i knew that it became personal.
So I started to search the allmighty internet. I found out that I can add telnet protocol in user prefs in Firefox. But it didn’t work. So I kept searching and finally I’ved put the bits and pieces together and solved the problem. Here it goes.

First thing to do is to tell Firefox that we WANT to use telnet:// links. To do that we must open Firefox and type “about:config” in address bar. And we create a new boolean preference (right click on an empty space), name it “network.protocol-handler.expose.telnet” and set the value “false” and restart the browser. That should be enough for Firefox to let us select an external application to open “telnet://” links.
From this point forward we can choose the easy way and choose putty or the hard way and use gnome-terminal/xterm/konsole. The “hard way” because telnet in terminal doesn’t know how to handle “address:port” format. So how should we do that ? Simple, we create a shell script and we use that script as the default application to open “telnet://” links in Firefox.

The script is pretty easy :


#!/bin/sh

address=`echo ${*##telnet://} | sed 's/:/ /g'`

#For xterm junkies :
xterm -e "telnet $address"

#For gnome-terminal users :
#uncomment the next line but comment
#all other terminal launchers (xterm, konsole)
#gnome-terminal -e "telnet $address"

#For konsole hipsters :
#konsole sends args separately to command so we use "" only for telnet
#uncomment the next line but comment
#all other terminal launchers (gnome-terminal, xterm)
#konsole -e "telnet" $address

And voila, sit back, relax and enjoy a cold beer…

Run remote procedures & GNS3

Dragos Draghicescu — Tue, 03 Nov 2009 11:11:53 +0000

An interesting and pretty new capability of Cisco IOS is scripting through TCL language. What is not that well documented is that you can configure a router in some situations and the interesting thing is that you can store the configuration procedure remotely, like on a tftp server for example. What I will present may be useful in lab environments, for simulation purposes. I used it to prepare a huge exercise for the CCNA 2 class.

First of all, I will suppose that you have configured a tftp server somewhere in your LAN. Second thing is you can configure a bridge between your Ethernet interface and a tap interface (a virtual interface, for use with the emulated router). In Linux, you can use the Bridge-utils and uml-utilities to do that. You can find a tutorial on how to do a bridge .

Now lets get to work!

In GNS3 (ran as root) you have to link the router with a clouds tap interface. In the cloud configuration panel, add a tap interface into the NIO tap tab (lets say tap0). Next, configure the router interface IP address like its part of your LAN. You can ping your gateway to verify that.

It’s all said and done. The script I wrote reads a number of Loopback interfaces to be configured from the user input. The output looks like this:

IOS output

The output is incomplete, but the script configured Loopback 0 to 4 with ip addresses.

I hope some will find what can be done with IOS TCL pretty interesting.

Good luck!

Wake on LAN

Dragos Draghicescu — Sun, 25 Oct 2009 21:43:35 +0000

As I was looking through the DD-WRT Linux distribution capabilities I have seen an interesting protocol named Wake on LAN, allowing one to power up a device remotely.

Basically, for implementation, you have to configure the BIOS on the PC (usually in Power Management section) to support it. After that, your network card will remain active even after you power off the PC, waiting in a low-power state for a “magic packet” to turn it back on. I managed to implement it in a lab and it’s really nice to have full control over configuring a host PC from turn on to shut down. And in a lab with 45 PC’s.. it kind of helps .

I’ve played a little with an embedded ARM device with Linux, and cross-compiled the program for use with the command line. The script that fires it lies . I apologise for not having around the latest version at the time writing this. It looks like this:

WOL_screen

You can look on the web for more information about WOL (it’s very well documented).

Good luck!