DHCP and mulitple default gateways

I just got this gripe... a user occasionally connects an Ethernet
interface on one or more of his hosts to a switch that's part of some
goofy private network. He has to connect to this network to access some
equipment that lives there, but he doesn't have a static IP. So, he
uses DHCP... and the DHCP server on that network hands out a default
gateway, which is major-stupid, because there's no router on that
network. I could start tilting at that windmill... or, I hope, find a
way to make sure that the default gateway assignment cannot clobber
existing settings.

Is there a way to "lock" a default gateway? Or specify that a default
gateway being assigned on an interface other than eth0 should be
ignored?

--
* John Oliver http://www.john-oliver.net/ *

On 08/22/2008 02:36 AM, John Oliver wrote:
> I just got this gripe... a user occasionally connects an Ethernet
> interface on one or more of his hosts to a switch that's part of some
> goofy private network. He has to connect to this network to access some
> equipment that lives there, but he doesn't have a static IP. So, he
> uses DHCP... and the DHCP server on that network hands out a default
> gateway, which is major-stupid, because there's no router on that
> network. I could start tilting at that windmill... or, I hope, find a
> way to make sure that the default gateway assignment cannot clobber
> existing settings.
>
> Is there a way to "lock" a default gateway? Or specify that a default
> gateway being assigned on an interface other than eth0 should be
> ignored?

I think, the appropriate answer to your question depends very much on
the DHCP Client in use on the said hosts e.g. I use isc-dhclient on
Debian/Ubuntu machines and shall edit the /etc/dhcp3/dhclient.conf
client configuration file.

--
Dr Balwinder S "bsd" Dheeman Registered Linux User: #229709
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Home: http://cto.homelinux.net/~bsd/ Visit: http://counter.li.org/

John Oliver <(E-Mail Removed)> wrote:
> He [the user] has to connect to this network to access some
> equipment that lives there, but he doesn't have a static IP. So, he
> uses DHCP... and the DHCP server on that network hands out a default
> gateway, which is major-stupid, because there's no router on that
> network.

Seems to me that the best solution is to fix the problem not the symptom.


> Is there a way to "lock" a default gateway? Or specify that a default
> gateway being assigned on an interface other than eth0 should be
> ignored?

You can tell your DHCP client (I use dhclient3) to ignore certain
settings. See dhclient.conf(5) and the "supersede" directive.

Chris