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8. FAQ

In this section I list some of the most frequently asked questions related to DNS and this HOWTO. And the answers :-) Please read this section before mailing me.

  1. How do use DNS from inside a firewall?

    A couple of hints: `forwarders', `slave', and have a look in the literature list at the end of this HOWTO.

  2. How do I make DNS rotate through the available addresses for a service, say www.busy.site to obtain a load balancing effect, or similar?

    Make several A records for www.busy.site and use bind 4.9.3 or later. Then bind will round-robin the answers. It will not work with earlier versions of bind.

  3. I want to set up DNS on a (closed) intranet. What do I do?

    You drop the root.hints file and just do zone files. That also means you don't have to get new hint files all the time.

  4. How do I set up a secondary (slave) name server?

    If the primary server has address 127.0.0.1 you put a line like this in the named.conf file of your secondary:

      zone "linux.bogus" {
        type slave;
        file "sz/linux.bogus";
        masters { 127.0.0.1; };
  };

    You may list several alternate master servers the zone can be copied from inside the masters list, separated by ';' (semicolon).

  5. I want bind running when I'm disconnected from the net.

    I have received this mail from Ian Clark <ic@deakin.edu.au> where he explains his way of doing this:

    I run named on my 'Masquerading' machine here. I have 
two root.hints files, one called root.hints.real which contains 
the real root server names and the other called root.hints.fake 
which contains...

----
; root.hints.fake
; this file contains no information
----

When I go off line I copy the root.hints.fake file to root.hints and
restart named.

When I go online I copy root.hints.real to root.hints and restart
named.

This is done from ip-down & ip-up respectively.

The first time I do a query off line on a domain name named doesn't
have details for it puts an entry like this in messages..

Jan 28 20:10:11 hazchem named[10147]: No root nameserver for class IN

which I can live with.
         
It certainly seems to work for me. I can use the nameserver for
local machines while off the 'net without the timeout delay for
external domain names and I while on the 'net queries for external
domains work normally

  6. Where does the caching name server store its cache? Is there any way I can control the size of the cache?

    The cache is completely stored in memory, it is not written to disk at any time. Every time you kill named the cache is lost. The cache is not controllable in any way. named manages it according to some simple rules and that is it. You cannot control the cache or the cache size in any way for any reason. If you want to you can ``fix'' this by hacking named. This is however not recommended.

  7. Does named save the cache between restarts? Can I make it save it?

    No, named does not save the cache when it dies. That means that the cache must be built anew each time you kill and restart named. There is no way to make named save the cache in a file. If you want you can ``fix'' this by hacking named. This is however not recommended.

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