Re: DNS Caching and resolv.conf

[Karl Hegbloom <hegbloom pdx edu>]

On Thu, 2005-12-15 at 13:02 -0600, Nathaniel R. Ben-Attar wrote:
> I just installed NM on my Ubuntu laptop and love it but have two issues.
> 
> 1.) Most important.  I have thusfar been using djbdns for caching a
> private TLD on the internal network at work.  I connect to the network
> via openvpn and under djbdns all I've had to do was create a textfile
> containing the authorative nameservers for each TLD on the network. 
> How do I do this under network-manager's BIND implimentation since it
> seems to be adamant about overriding and killing my djbdns?  Or better
> yet, can I just kill off BIND and use what works for me?
> 
> 2.) Ubuntu uses dhclient and I've had a custom search path dynamicly
> added to resolv.conf by dhclient to make resolving hosts I use
> regularly easier.  Judging by the resolv.conf that NM creates I can
> saely assume that it does NOT use dhclient and therefor I would like
> to know how to specify a search line to be inserted into resolv.conf

Both of those issues could be eliminated if NM was 'resolvconf' aware.
The problem I had when I tried to fix that, a month or two ago, was that
the call to resolvconf needs to be told the interface that the
"resolv.conf" data is to be associated with.  To get the interface at
the point in the program where it makes sense to call 'resolvconf', you
have to traverse some data structures... but you can't get there from
here.  IIRC, a pointer would need to be added to a struct, or something.
I ran out of time when someone else ran out of patience.

Perhaps someone more familiar with NM, from the Debian camp, can see how
that could be done without destabilizing or "breaking encapsulation"...
().

The reason resolvconf fixes that is that the dhclient script runs hook
scripts, and one of them was put there by resolvconf.  It deals with the
DNS information gathered by dhclient, adding the staticly configured
nameservers given in dhclient.conf.  (yet another location for such
information, though it's configuration syntax probably allows it to
differ depending on what network responds to the dhclient query so maybe
that really is where it belongs?... else in NM?)

I wonder if there are similar systems in other distros that could use
the similar information at some point in their configuration process?

I never completely "got" the argument wrt why Bind is better than any
arbitrary local DNS cache.  It had something to do with security issues
surrounding VPN.  I wish that for the holiday, someone would write up a
decent explanation for us, and/or post the URL to such on the list.
(TIA)

Some have argued that 'resolvconf' is too unpredicable due to it's use
of the 'hook script' design pattern.  The thing is that there really are
not that many programs that require it's functionality.  Not that many
programs need to deal with updates to the /etc/resolv.conf file.  Since
it's rare that a new program comes along requiring that, it does not
have to scale up.  'resolvconf' provides an API for changes to the
resolv.conf file.

-- 
Karl Hegbloom <hegbloom pdx edu>