DNS Ports

[Dave Harman]

Thanks for your reply.

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

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

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.

Is my understanding correct ?

Thanks

Dave Harman



-----Original Message-----
From: bind-users-bounce at isc.org [mailto:bind-users-bounce at isc.org]On
Behalf Of Barry Margolin
Sent: Monday, July 21, 2003 11:27 AM
To: comp-protocols-dns-bind at isc.org
Subject: Re: DNS Ports


In article <bfhalf$1e70$1 at sf1.isc.org>,
Dave Harman <dharman1060 at earthlink.net> wrote:
>Hi, NG
>
>I am using BIND 9.2.1-16, the one that comes with RedHat 9
>I am setting up Iptables and I am having difficulty in finding out
>exactly what ports Bind uses to send and receive queries and data.
>
>I know DNS uses UDP to send and get data.
>
>Does DNS always use the unprivileged ports to send queries ?

It uses an unprivileged local port, unless you override this with a port
specification in the query-source option.

>Does DNS always receive answers and quesies on port 53 ?

It receives queries on port 53, it receives answers on the port that was
used when it sent out the query.

>Does the resolver use different ports than the DNS server ?

Yes, otherwise the system wouldn't know whether the answer should be sent
to the server or the resolver.

--
Barry Margolin, barry.margolin at level3.com
Level(3), Woburn, MA
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