From: Abu Hamzah (hamzah.abu@gmail.com)
Date: Thu Dec 07 2006 - 10:22:28 ART
OK, that's great background, thanks.
So, if a client query can not be answered by the 1st resolver does this
query get directed to the second resolver or is the 1st resolver going get
the query info from the second resolver? Just want to be clear how
un-resolved queries are dealt with...
thanks again.
On 12/7/06, Frank <ocsic@web.de> wrote:
>
> Abu Hamzah schrieb:
>
> Zone transfer is between dns servers to transfer zone informations. This
> must be
> a reliable process so it uses tcp port 53. udp port 53 is used for
> sending out dns information
> for clients. Clients send dns queries to servers on port 53 udp. Most
> queries are udp based.
> Exept queries lager than 512 bytes are send as tcp.
>
> http://www.faqs.org/rfcs/rfc1123.html
>
> 6.1.3.2 Transport Protocols
>
> *DNS* resolvers and recursive servers MUST support *UDP*, and
> SHOULD support *TCP*, for sending (non-zone-transfer) queries.
> Specifically, a *DNS* resolver or server that is sending a
> non-zone-transfer query MUST send a *UDP* query first. If the
> Answer section of the response is truncated and if the
> requester supports *TCP*, it SHOULD try the query again using
> *TCP*.
>
> *DNS* servers MUST be able to service *UDP* queries and SHOULD
> be able to service *TCP* queries. A name server MAY limit the
> resources it devotes to *TCP* queries, but it SHOULD NOT
> refuse to service a *TCP* query just because it would have
> succeeded with *UDP*.
>
> Frank
> > Hi all
> >
> > Can someone please clarify how UDP and TCP DNS port 53 is used?
> >
> > I know that when we try to connect to a website we use UDP DNS port 53.
> > Also, when a name server is doing Zone transfers it uses TCP port 53 for
> DNS
> > Zone transfer. How about, if we connect to a name server1 for resolving
> say
> > www.abc.com and this server1 can't resolve the name then does server1
> use
> > TCP port 53 for DNS to and get this from server2?
> >
> > Any good URL for this background info would be appreciated.
> >
> > thanks
> >
> > Abu Hamzah
> >
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