Tag Archives: Perl

Hostcheck

I continue to publish some my coding.

Hostcheck is a simple Perl script that can be useful to quickly check if a list of host is up.
It just read a host file and check if the host are available doing a ping test or trying to open a socket.

Nothing great, but it may help to quickly check that most of things are right after a network change, for instance.
Because we want to test many hosts, and not to scan, the pace is fast so it may not be 100% reliable. The idea is to see roughly is the connectivity is correct or if your whole LAN is down.
It uses colors and is easy to read, so it might be good to show to your manager ! :)

I hope it will be useful. More info and download link are there.

Perl : how to monitor a service remotely using sockets

I came to program my first Perl script based on sockets, after setting an IPSEC tunnel.

This tunnel is linking the remote peer and the local peer through an OpenBSD VPN gateway (managed with Isakmp).

The problem is that time allowed for this connection is limited, for security policy reasons. So it is not a 24- hour standard tunnel, but rather an on-demand type connection.

Note that the connection is automatically reset by the remote peer, by invalidating the connection cookie and therefore oblige to renegotiate the VPN tunnel from the beginning (phase 1 of the key exchange).

In other words, the Isakmp service has to be restarted every time we need the tunnel to be up.

Of course, it is not the purpose of Isakmp to have such a mechanism and what we want is to start the tunnel from the local peer, every time it needs to do some transfer.

The graph below summarizes the situation :

IPSEC tunnel with OpenBSD as a VPN gateway

That is why I came to develop a script that opens a socket and allows the peer to remotely restart the Isakmp service.

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How to strip the attachment from an IMAP mail

While trying hard long and long hours to write a perl script that can extract attachments from pieces of e-mail, I realized that there were no clear info on the web on how to do, and that if I successed, I would publish that script.

Finally I succeded. That is actually very easy and that is probably why nothing was ever published about it. But, when you are a beginner in Perl (I learned it in 1 week), you normally need a little bit more help. Also, I was not alone in that case and there were a numerous questions on various forum, but without satisfying answers.

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