Configure your ubuntu desktop as an internet gateway

I have a 3g mobile stick and in certain circumstances I would need to route internet traffic of a PC/server or a particular subnet through this interface. In a windows OS we could simply achieve this by enabling internet sharing on the interface itself. But in the case of ubuntu we can easily enhance ICS (internet connection sharing) feature to a higher level as internet gateway. This way your linux machine can be turned into a gateway which is way cool, isn’t it?

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Cisco IP Phones 79XX with Asterisk

 

 

Recently we had a pack of cisco 7942G phones that we were required to get them up running with Asterisk. The good thing about 79XX series is that they all support SIP besides SCCP. Whereas, the bad thing is that they are by default running on SCCP and you have to upgrade them to SIP first. I spent a great deal of time trying to figure this out, as I were going to use SIP Version 8 and there is no to-the-point documentation (at least not that I could find!)

 

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Linux File Discriptors

The Standard UNIX File Descriptors – Standard Input (stdin), Standard Output (stdout), and Standard Error (stderr). Bash and other modern shell provides I/O redirection facility. There are 3 default standard files (standard streams) open:
[a] stdin – Use to get input (keyboard) i.e. data going into a program.

[b] stdout – Use to write information (screen)

[c] stderr – Use to write error message (screen)

You can look at /usr/include/unistd.h if you forget them:

/* Standard file descriptors.  */
#define STDIN_FILENO    0   /* Standard input.  */
#define STDOUT_FILENO   1   /* Standard output.  */
#define STDERR_FILENO   2   /* Standard error output.  */
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