Caching DNS for dialup

[David Jenkins]

On Mon, 29 November, 2004 20:44, Jonathon McKitrick said:
> On Wed, Nov 24, 2004 at 05:07:20PM +0000, Peter Risdon wrote:
> : A caching DNS server would help conserve bandwidth on a dialup
> : connection - I generally run one myself with any connection with
> limited
> : bandwidth.
>
> After RTFM, I believe I have it up and running.  ;-)
>
> Named is running, but how can I be sure the caching is working?
>
> Also, does it make sense to do this on each box, or just the gateway?

You can try a few digs and see what the response time is.

i.e. pick a hostname that you know you haven't visited since the
caching DNS server has been running. Then do a dig.

>From the gateway.

# dig @localhost somehostname

then do it again, and see how different the response time is.

e.g. on mine:

> dig @localhost www.bbc.co.uk

<snip>

;; Query time: 59 msec
;; SERVER: 127.0.0.1#53(localhost)

and then again ...

;; Query time: 2 msec
;; SERVER: 127.0.0.1#53(localhost)

then try this from your client machines on your network (with
different domain names etc...)

This is a very simple way of doing it.

Of course, you could also sniff the gateway's external network interface
for DNS traffic and try a hostname you know you should have in your
cache.

In my case:

# tcpdump -i xl0 port 53

There's probably loads of better ways of doing it, but these are nice
and simple.

Cheers,
David