ISP wont tell me DHCP server address; Any logic to his stance?

[bgunn]

Hi All

We have just connected to ADSL and I am putting together a firewall script. I am using the one that appears in the "Iptables Tutorial" by Oskar Andreasson. To use this script I need to know the IPaddress of the ISPs DHCP server (to ensure that incoming DHCP packets are in fact from this server). I have contacted the ISP and asked them for this address, but they immediately get suspicious and say that it is secret.

I tried to explain to them that as one of their customers I am already connecting with that very server, so can't see why they would need to keep it a secret. So far no luck. I am trying to talk directly with the System Administrator - hopefully he will see reason - but up until now I have been unable to talk with him.

I kind of feel like I am banging my head on a brick wall with this one. Can someone please tell me: is there any reason why they should not tell me the DHCP IP address or are they being unreasonable? If I am currently getting a dynamic address each time I connect, is there some way I can query the DHCP server name while connected?

Thanks, Ben

[jumpedintothefire]

Which dhcp client are you using??

With dhcpcd, the server's address is saved in a file /etc/dhcpc/dhcpcd-ethX.info (replace the X with the correct interface for your system)

example:
-------------
IPADDR=24.79.xx.xxx
NETMASK=255.255.252.0
NETWORK=24.79.8.0
BROADCAST=24.79.11.255
GATEWAY=24.79.8.1
HOSTNAME=h24-79-xx-xxx
DOMAIN=wp.shawcable.net
DNS=24.66.94.195,24.66.94.212
DHCPSID=24.66.94.195
DHCPGIADDR=24.79.8.1
DHCPSIADDR=24.66.94.195
DHCPCHADDR=00:A0:4B:04:D5:E0
DHCPSHADDR=00:00:77:94:69:40
DHCPSNAME=
LEASETIME=172800
RENEWALTIME=86400
REBINDTIME=151200

------------------------------------

note the dhcpserver's ip and mac addresses.......

There should be a record from your dhcp client, somewhere on the drive....

[Alex Cavnar, aka alc6379]

I think that jumpedintothefire's on the right track, but I thought I might provide an explanation as to why the DHCP server's address is a "secret":

When you called your ISP, you probably got a "peon" in tech support. Normally, they don't know anything but to tell you how to "click on the Start menu, select Shut Down..., select Reboot, and hit OK"

They probably didn't know the IP of it, but didn't want to come off as sounding stupid.