[PLUG] resolve.conf file
Carlos Konstanski
ckonstanski at pippiandcarlos.com
Sun Dec 27 18:39:24 UTC 2009
On Sun, 27 Dec 2009, Denis Heidtmann wrote:
> Date: Sun, 27 Dec 2009 10:10:59 -0800
> From: Denis Heidtmann <denis.heidtmann at gmail.com>
> Reply-To: "General Linux/UNIX discussion and help; civil and on-topic"
> <plug at lists.pdxlinux.org>
> To: "General Linux/UNIX discussion and help, civil and on-topic"
> <plug at lists.pdxlinux.org>
> Subject: [PLUG] resolve.conf file
>
> I mentioned earlier that I was having trouble with a new dsl modem's
> behavior as a dns server. That has been resolved by avoiding dhcp.
> This was accomplished with the help of a visiting geek (my son).
> Resolveconf was installed; dns addresses set statically,
>
> As best as I can determine, everything is working fine. But I seek
> some understanding. The resolv.conf contains some entries which make
> no sense to me. The visiting geek is no longer interested in these
> questions, as it is no longer broken. So I appeal to you.
>
> resolv.conf:
>
> # Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
> # DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
> nameserver 192.168.0.1
> nameserver 69.64.224.67
> nameserver 69.64.224.66
> search domain.actdsltmp
>
> I expect that the nameserver 192.168.0.1 entry is left over from
> earlier dhcp responses. (Visiting geek's Debian machine has only the
> two valid nameserver entries in his file--he had not run a dhcp
> client.) Why does it persist in this file? And why does it not break
> dns searches occasionally? If I run dig repeatedly, only the
> 69.64.224.67 address seems to get used. If I force use of
> 192.168.0.1, it fails, as expected.
>
> What does "search domain.actdsltmp" do? Is domain.actdsltmp a valid name?
>
> Should I attempt to clean up this file? If I should, how might that be done?
>
> Thanks for any education you can throw my way.
>
> -Denis
192.168.0.1 is most likely the IP address of your DSL router. I never
used resolvconf, but if it's writing this file, then I'll bet that
there is some sort of DNS server running on the router. Run the
following command from a root shell (it will take a long time to run):
nmap -sU 192.168.0.1
If you see UDP port 53 listed as open, then there is a DNS server
running on the router. (If you see port 68, that's the DHCP server.)
If this is true, it would be in your best interests to get it working
properly, and use it instead of going directly to the ISP DNS
servers. The local DNS server should be doing lookups on behalf of all
users on your LAN, and caching the results for faster speed and less
internet chatter.
The "search" line is for when you attempt to resolve a
non-fully-qualified hostname. For instance, my local domain is
pippiandcarlos.com, and this is reflected in my resolv.conf file as
"search pippiandcarlos.com". If I try to "ping ns", it will be
converted to "ping ns.pippiandcarlos.com".
I hate to be a party pooper, but I still feel that using resolvconf
and static IPs is a bandaid that will continue to peel off when
wet. The right thing to do is to get your own DNS and DHCP servers
(the ones on the DSL router) working properly. Of course these DSL
modems are notoriously crappy, and it is quite possible that fiddling
with its configuration will have no effect. That's why I use cable and
my own linux box as a router/firewall. Cable modems do not contain
router/firewalls; they simply pass the connection through. The last
DSL modem I had was an Actiontek which did not respond to any of my
attempts to configure it. Qwest refused to replace it. They told me I
could buy my own. Customer exits stage.
Carlos
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