Subject: [Enum] Processing of 'Additional Information Section'

From: [email-masked]
Date: Mon, 10 Jul 2006 09:47:34 +0530

Hi,

I have a question on the use of 'Additional Information Section' of a 
given DNS response.

RFC 3761 say that the clients are encouraged to check for additional 
information present in the response.

When we query for an e164 number, we will get AORs associated with 
different services. In case the client supports that service, it will 
fetch contacts and perform SRV/A lookup. My question is what additional 
information the NAPTR response contain? Do the current DNS servers support 
additional information section? Can anyone suggest a place where I can get 
a detailed information about the processing of additional information 
section ? Whether it is important to process this additional information 
section?

Regards,
Prashant

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From: Patrik Fältström <[email-masked]>
Date: Fri, 14 Jul 2006 14:52:21 -0400

On 10 jul 2006, at 00.17, [email-masked] wrote:

> information the NAPTR response contain?

Depends on what the server choose to put there. For "normal" use of  
NAPTR+SRV, it normally include the SRV records.

Here is one example:

pingu>dig outgoingproxy.yxa.frobbit.se. naptr

; <<>> DiG 9.2.2 <<>> outgoingproxy.yxa.frobbit.se. naptr
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 60887
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 2, ADDITIONAL: 5

;; QUESTION SECTION:
;outgoingproxy.yxa.frobbit.se.  IN      NAPTR

;; ANSWER SECTION:
outgoingproxy.yxa.frobbit.se. 900 IN    NAPTR   10 0 "s" "SIP+D2T" ""  
_sip._tcp.outgoingproxy.yxa.frobbit.se.
outgoingproxy.yxa.frobbit.se. 900 IN    NAPTR   10 0 "s" "SIP+D2U" ""  
_sip._udp.outgoingproxy.yxa.frobbit.se.
outgoingproxy.yxa.frobbit.se. 900 IN    NAPTR   10 0 "s" "SIPS+D2T"  
"" _sips._tcp.outgoingproxy.yxa.frobbit.se.

;; AUTHORITY SECTION:
frobbit.se.             520     IN      NS      ns.cafax.se.
frobbit.se.             520     IN      NS      ns1.frobbit.se.

;; ADDITIONAL SECTION:
sip.frobbit.se.         900     IN      A       193.109.175.117
ns1.frobbit.se.         877     IN      A       66.125.125.88
_sip._tcp.outgoingproxy.yxa.frobbit.se. 900 IN SRV 0 0 5066  
sip.frobbit.se.
_sip._udp.outgoingproxy.yxa.frobbit.se. 900 IN SRV 0 0 5066  
sip.frobbit.se.
_sips._tcp.outgoingproxy.yxa.frobbit.se. 900 IN SRV 0 0 5067  
sip.frobbit.se.

;; Query time: 124 msec
;; SERVER: 132.219.0.11#53(132.219.0.11)
;; WHEN: Fri Jul 14 14:45:33 2006
;; MSG SIZE  rcvd: 428

> Do the current DNS servers support
> additional information section?

Absolutely.

> Can anyone suggest a place where I can get
> section ?

It is up to you as a client to use that data if you want to.

> Whether it is important to process this additional information
> section?

It minimizes the number of queries sent to the DNS. On the other  
hand, you should not blindly trust what is in there (because it might  
be fake data, and if you cache it you might get so called cache  
posioning), just like you should/can not trust any data from DNS if  
it is not the case you use DNSSEC, in what case both answer and  
additional data in the response can be verified.

Description of the various sections of queries and responses for DNS  
in laid out in any book on DNS.

    Patrik