Re: DNS over TCP: Order of responses

There is no order specified in RFC1035 that I can find.

Section 4.2.2 states:

Several connection management policies are recommended:

   - The server should not block other activities waiting for TCP
     data.

   - The server should support multiple connections.

   - The server should assume that the client will initiate
     connection closing, and should delay closing its end of the
     connection until all outstanding client requests have been
     satisfied.

   - If the server needs to close a dormant connection to reclaim
     resources, it should wait until the connection has been idle
     for a period on the order of two minutes.  In particular, the
     server should allow the SOA and AXFR request sequence (which
     begins a refresh operation) to be made on a single connection.
     Since the server would be unable to answer queries anyway, a
     unilateral close or reset may be used instead of a graceful
     close.


So it seems to imply that each query is a unique, separate transaction 
just like with UDP. They can be responded to in any order.

		--Dean




On Sun, 8 Mar 2009, Dwayne C. Litzenberger wrote:

> When communicating over a TCP connection, are DNS servers expected to send 
> responses in the same order as it received the corresponding queries, or is 
> something like the following allowed?
> 
>       Resolver                                Nameserver
>       --------                                ----------
>       QR=0, ID=1000 example.com IN A ---->
>       QR=0, ID=1234 heaven.af.mil IN A ---->
>            <---- QR=1, ID=1234 heaven.af.mil IN A 10.0.0.1
>            <---- QR=1, ID=1000 example.com IN A 10.0.0.2
> 
> I'm writing a small DNS server that forwards queries to other servers based 
> on the contents of the query (QNAME, RD, etc.) so I need to know how both 
> the resolver side and the nameserver side _should_ behave, as well as what 
> I can expect from other software.
> 
> I didn't find anything in either RFC 1035 or RFC 2181 about this.  Any 
> insights would be much appreciated.
> 
> Thanks,
>    - Dwayne
> 
> 

-- 
Av8 Internet   Prepared to pay a premium for better service?
www.av8.net         faster, more reliable, better service
617 344 9000