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 [...]
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 this connection is limited time, for access right reason. So it is not a 24 hours standard tunnel, but rather an on-demand type connection.
Note that the connection is automatically reseted by the remote peer, by invaliding the cookie of the connection and therefore obliging to renegotiate the VPN tunnel from the beginning : phase 1 of the key exchange.
In one word, the Isakmp service has to be restarted every time we need the tunnel to be up.
Of course, this is not the purpose of Isakmp to have such a mecanism and what is interesting 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 why I came to develop a script that listen on a socket and allow that peer to remotely restart the Isakmp service.
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.
