multiple DHCP servers and /etc/resolv.conf

[Vincent Lefevre <vincent@vinc17.net>]

My Debian laptop has several ways to have network connection: Ethernet,
wifi and USB (the latter is used together with my Nokia N900, which has
a DHCP server). I have the following problem, when doing:

1. Connect via wifi, using DHCP (as usual). /etc/resolv.conf is
   modified accordingly, as expected.

2. Connect my Nokia N900 via USB, also using DHCP. The problem is
   that /etc/resolv.conf is overwritten, and if I do not enable wifi
   or GPRS/3G connection on my N900, DNS resolution no longer works.
   Overwriting /etc/resolv.conf is expected when there is only the
   USB connection (the N900 being used as a router, so that I can
   get an Internet connection via GPRS/3G when no wifi hotspots are
   available); otherwise it should not be modified, IMHO.

Does anyone have any solution that does *not* require manual changes
(when I want to change the way I connect)?

I've seen some possible solution on

  http://serverfault.com/questions/223427/dhclient-append-settings-from-multiple-dhcp-servers

but clean-up (not mentioned there) appears to be complex. In my case,
I don't think I need a merge. The following behavior should be OK, if
possible: if there is already a default route, then the DHCP client
should not modify "/etc/resolv.conf".

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Vincent Lefèvre <vincent@vinc17.net> - Web: <http://www.vinc17.net/>
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