Re: Simple DNS Record A

["Robert N. M. Watson" <robert.watson@xxxxxxxxxxxx>]

On 26 Jul 2011, at 12:48, Éireann Leverett wrote:

> Ah! I had that 'recursive' model wrong. I thought each server contacted the 
> next up the chain, now I can see all those little inefficient loops in a 
> recursive resolver...and hence motivating the Main Name Service thesis.
> 
> OK, I'll get a socket opening and closing on a timeout for some coding 
> practice, but keep reading the DNS queries message diagrams to understand the 
> resolver pseudo-code mainly.

Can I suggest some practical experimentation here? There's nothing like getting 
your hands dirty :-).

The first tool you should know about is dig(1), which is a command line DNS 
query tool. You can ask it to do recursive/non-recursive lookups, get traces of 
communication, etc.

The second is tcpdump, which I feel certain you've used before, but quite 
useful for seeing what actually goes out. Wireshark might have better packet 
parsing, and you can also write out dumps with tcpdump and read them with 
Wireshark, etc.

The third is bind -- if you start up a local name server on your box, you can 
query its cache, trace it's transactions, and so on.

(If for some reason this isn't possible on your box, perhaps some argument 
about security or something, we can work out an alternative system for you to 
play with).

All of these will be useful when you're experimenting with DNS in Mirage, since 
you'll want to trace its interactions with the name server, compare queries you 
construct with what it comes up with, and so on.

Robert