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[ale] ATT Broadband and DHCP Help Requested

On Sat, May 19, 2001 at 12:43:21PM -0400, Jeff Dilcher wrote:
> Hello,

> (Apologies if this went out a couple of days ago-
> I have been having a bit of difficulty joining the
> group.  I hope this hasn't been discussed recently...)

> I am an ATT cable subscriber in Dekalb county.
> Formerly Mediaone.

> I am trying to configure my Redhat 7.0 box
> to run a script (which will update Zoneedit.com,
> update my firewall script, etc.) when my machine 
> obtains a new ip lease.

> How would I ensure that a script is kicked off
> when I get a new IP address?

	First off...  If you are using "pump", DITCH PUMP!

	Use dhcpcd.  When dhcpcd gets a new lease is runs a script
/etc/dhcpc/dhcpcd-$IFACE.exe and that's where you can do your address
checking.  All the data is stored in /etc/dhcpc/dhcpcd-$IFACE.info in
"shell sourcible" form.  For example, if your interface is on eth0,
you just run ". /etc/dhcpc/dhcpcd-eth0.info" and then "IPADDR" has
your IP address and GATEWAY has your gateway.

	What I do is copy that to a backup, /etc/dhcpc/dhcpcd-$IFACE.info~,
and then compare the two.  If addresses change, then I update my DNS
(using dynamic DNS) and IPSec (I use this with a VPN between several

	Things to watch out for, though...  AT&T lately has had some serious
brain farts and your interface will come up in a default, unroutable, state.
then you can't update jack shit anywhere.  DON'T hang the interface by
trying to update stuff.  If you fail to update information on the net,
you have to be sure and come back later when the interface stabilizes,
even if the address doesn't subsequently change.  (I guess the best idea
would be to not back up the .info file unless and until you could update
your DNS).  You may need to back some of this up with a cron job in case
your script fails to update your DNS and it doesn't get rerun later when
routing stabilized and the address doesn't change.

> Also, I am setting up some firewall rules, and 
> trying to be conservative.  However, I don't want
> to block my dhcp client from talking to the dhcp server
> altogether.  Can anyone tell me what ports need 
> to be open for ATT to communicate via dhcp and 
> give my machine it's new IP?  Any caveats I should
> be aware of, in regards to DHCP, when configuring
> the firewall?
> Thanks!!
> Jeff

 Michael H. Warfield    |  (770) 985-6132   |  mhw at WittsEnd.com
  (The Mad Wizard)      |  (678) 463-0932   |  http://www.wittsend.com/mhw/
  NIC whois:  MHW9      |  An optimist believes we live in the best of all
 PGP Key: 0xDF1DD471    |  possible worlds.  A pessimist is sure of it!

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