DNS Ports

[Dave Harman]

Thanks for your reply.

May I ask a further question.
As I understand it, the default for BIND 9 servers
is to send queries out on unpprivileged ports to the remote
server's port 53. 

The remote server sends the reply from it's port 53
to the unpriviliged port the local server used to send the query.

IS this correct ?

Thanks

Dave Harman

-----Original Message-----
From: bind-users-bounce at isc.org [mailto:bind-users-bounce at isc.org]On
Behalf Of Herb Martin
Sent: Saturday, July 26, 2003 5:25 PM
To: comp-protocols-dns-bind at isc.org
Subject: Re: DNS Ports


> So, as I understand it, the resolver sends out queries
> on an unpriveleged port and receives the answer on the
> same port.

That is normal, to server on 53 and from server on 53
from/to the clients chosen port.

> Does the resolver cache the reply, or the DNS server ?

Depends on the resolver -- and settings.  Starting with Win2000
Microsoft clients BEGAN caching by default -- this is most
useful for stand-alone dial-up clients with no local DNS server
and relatively slow WAN links.

Older DNS clients tended not to cache.

Traditionally DNS servers have cached recursive lookup info
(things they found out in servicing clients) and the actual info
they sought.

Both can be disabled, depending on the server of course.

> The DNS server listens for queries from resolvers on port 53
> and sends a reply on the the same port the resolver used in the query.

Normally.  Changing this is senseless as most clients would never
find the server -- it is only done for "test beds", like when developers
are testing a "funky" server.

> Is my understanding correct ?

yes