DNS unreliable with a Linksys ADSL2MUE adsl modem

[neil woolford]

I have a Linksys ADSL2MUE modem, connected to a Linksys WRT54G
wireless/wired router.

When I first set this up, back in May this year, I found that there was
a problem with DNS and DHCP using Ubuntu (Hoary back then, Breezy now).

I have set the modem to act as a DHCP server, this hands out address
leases to wired and wireless machines without apparent problems.  It
also sets the DNS to its own address (192.168.1.1).  If my laptop is
running Windows 98 this works fine.  Under Ubuntu I don't get a DNS
service on any of my machines.

The fix that has worked for me so far is one that others have also used
with this and other modems, it is to edit /etc/dhcp3/dhclient.conf so
that the line "prepend domain-name-servers" is uncommented (active) and
fill in the domain name servers you wish to use in that line.  This fix
works, as the DNS addresses entered here are placed before the modem's
DNS address and are therefore tried first.  However it isn't exactly
elegant, and if the servers you have entered aren't available then there
is no fallback.

I recently found a link which suggests a more elegant method.
http://johnwilger.com/articles/2005/12/13/ubuntu-5-10-breezy-badger-update-dns-when-obtaining-dhcp-lease-on-windows-network

Basically what is suggested is to edit dhclient.conf so that the line
with "send host-name" is uncommented and set to your hostname.  For me
the following line works fine.

send host-name "localhost.localdomain";

Naturally this also works with the actual literal hostname.

Fine so far;  I am now obtaining my DNS service from the modem, which is
patching me through to the DNS provided by my ISP.  If they change the
DNS addresses, the modem should be updated by them and all will continue
to work.  Nice.

My problem?  This works on the first machine I tried it on, but not on
the subsequent two (both also running Breezy).  They still require the
cruder fix of prepending fixed DNS addresses.  Does anyone have any idea
what might be going on here?

Neil

PS  Thanks to Cory Burger for updating the modem howto information on
the wiki.  It is now well cool and made reinstalling a mate's EP536
modem much easier.
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