Bind8 on dial on demand system

[Kevin Darcy]

Patrick-Thomas Chmielewski wrote:

> Hi All,
>
> I was trying Bind8.2.2 on my Computer, which uses dial on demand conection
> to the internet. It is configured to forward only. My problem is, that bind
> opens a connection to the internet, when started. I've found following line
> in one of my log-files after I turned off dod:
> named[856]: sysquery: sendto([160.45.10.12].53): Network is unreachable
> So it seems that binds tries to connect to one of my forwarders-dns
> although there was no request from one of my computers in lan.
> How can I turn off this initial query?

There's no way to turn off the initial query. BIND is trying to "prime", i.e.
get a good set of root NS records, in order to build its in-core database.
This is integral to the code and I understand would be very difficult to
change.

The only reasonable solution I've been able to come up with (but have had no
occasion to implement myself) is to have 2 different BIND config files, one
for when you are connected to the Internet, and one for when you are not, and
switch between them. The "disconnected" config would define the server as
master for the root zone, so it would never need to "prime".

> It also seems that bind tries to update things allready in cache. Is there
> a way to turn this off, too?

I'm not sure what you mean by "update things already in cache". Cache entries
don't last forever -- it is perfectly normal for them to expire periodically
and thus for the nameserver to have to query them again.

> Because my computer is not turned on 24h/day I'm looking for a way to save
> bind's cache to disk when turning off an loading from disk when turning on.

To repeat: cache entries expire. For this reason, not a lot of effort has been
put into saving the cache to disk and reloading it on startup, because you'd
have to store timestamps and purge the expired records when reloading. This is
a non-trivial task and could greatly impact startup time.

> Is there a way to save the ip of frequently visited pages so that bind have
> not to look up using the forwarders?

If the records have reasonable TTLs on them, then you won't be bothering with
the forwarders much anyway since the records will usually be in your cache
when resolvers ask for them. The only other alternative that comes to mind
would be to set up master zones containing these "popular" names and somehow
keep them always in synch with the real zones. This seems like more trouble
than it's worth.


- Kevin