[Linux-Discussion] Re: DHCP Server Detection
- From: "David A. Wallace" <dwallace@xxxxxxxxxxx>
- To: <linux-discussion@xxxxxxxxxxxxx>
- Date: Wed, 28 Aug 2002 13:39:56 -0500
> -----Original Message-----
> From: linux-discussion-bounce@xxxxxxxxxxxxx
> [mailto:linux-discussion-bounce@xxxxxxxxxxxxx]On Behalf Of John Madden
> Sent: Tuesday, August 27, 2002 9:37 PM
> To: linux-discussion@xxxxxxxxxxxxx
> Subject: [Linux-Discussion] Re: DHCP Server Detection
>
>
>
> > The problem is that they have a M$ DHCP server in the lab that they
> > occasionally need to turn on for the W2K classes. I would like to write
> > a cron job script that will bring the my box's DHCP service down when
> > the M$ DHCP server comes up.
>
> Can the MS folks be given their own subnet (or even physical
> segment), and
> only answer DHCP queries for their own machines? Especially if this is a
> lab environment where they'll be playing with stuff, and even moreso
> because it's an MS DHCP server (think active directory, non-RFC stuff,
> etc.), I don't think you'd want to be bringing your own DHCP box up and
> down all the time, unless it's not a big deal that the machines have no
> connectivity at times. I honestly don't know how well
> already-leased IP's
> get transferred from one client and server to another - YMMV.
The MS folks have their own physical segment and use their own private IP
address range. That is why I built them a simple firewall/nat box. The box
let's them have outside connectivity with their private addresses and also
keeps their their M$ DHCP server from answering requests coming from our
network.
We have a DHCP server that services the Region. This is not the box I was
talking about bringing down. I'm going to add dhcpd to the firewal/natbox
that sits between their network and ours. It will only hand out private
addresses for their segment. They need it's service about 3/4 of the time,
but there will be time periods (weeks at a time) that they need to
exclusively use their DHCP server. That's why I would like the Linux box to
occasionally check to see if the M$ server is up.
>
> > My thinking is that I could write a cron job script to occasionally
> > check port 68 on the M$ DHCP server. If the port is active the script
> > would bring the Linux DHCP down. If the port isn't answering DHCP
> > requests it would bring the Linux DHCP service up.
>
> (Isn't it port 67?)
>
>
67 and 68 one is server side, one is client side. Maybe I have them
backward.
> #!/usr/bin/perl -w
> use strict;
> use IO::Socket;
>
> my $sock = IO::Socket::INET->new(
> PeerAddr => 'ms-crapper',
> PeerPort => '67',
> Proto => 'udp') || exit;
>
> print "Killing dhcpd...\n";
> system("killall -15 dhcpd");
>
>
> The idea is that if a socket doesn't exist, we just exit (you may want to
> add code there to make sure dhcpd is still running at this point, in case
> we've previously killed it), and otherwise, we kill off our own dhcpd.
>
> John
>
>
>
>
Cool. This gives me something to start off with. I'm getting a little handle
on shell scripting, but since I'm still relatively new to much of this, I'll
have to figure out the perl side of things. I appriciate the help. If you
think of anything else please let me know.
Thanks again,
David
>
> --
> # John Madden weez@xxxxxxxxxxxxx ICQ: 2EB9EA
> # FreeLists, Free mailing lists for all: //www.freelists.org
> # UNIX Systems Engineer, Ivy Tech State College: http://www.ivytech.edu
> # Linux, Apache, Perl and C: All the best things in life are free!
>
>
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