bind9 fills in the 'additional' section when doing a query?

[Mark_Andrews at isc.org]

> 
> Hello all,
> 
> I've just noticed that the query behaviour of bind9 vs bind8 (and
> bind4) is different.  Prior to bind9.2, a netsnoop reveals no
> "additional" section in a query:
> 
> Bind4 or bind8:
> 
> 0000:   len   84   time 12:00:59.415373
>     ether:  
>             type ip    
>     ip:     v 4       hl 5      tos 0     len 70    id 26925  off 0
>             ttl 60    p udp     sum 0xf2c3
>             src x.y.z                     dst a.b.c
>     udp:    sport 53 (dns)                dport 53 (dns)              
>             len 50    sum 0x9ec4
>     dns:    id 39831  qr 0 (query)        opcode QUERY        aa 0      tc 0
>             rd 1      ra 0      unused 0  rcode NOERROR       qdcount 1 
>             ancount 0           nscount 0           arcount 0 
>     dns.questions:
>             name setd-ctl.nawcad.navy.mil                                    
>             type A              class IN   
> 
> 
> 
> bind9:
> 
> 0000:   len   82   time 12:02:46.488963
>     ether:  
>             type ip    
>     ip:     v 4       hl 5      tos 0     len 68    id 32780  off 0
>             ttl 56    p udp     sum 0x6aa7
>             src d.e.f.g              dst a.b.c
>     udp:    sport 34339                   dport 53 (dns)              
>             len 48    sum 0x4547
>     dns:    id 48423  qr 0 (query)        opcode QUERY        aa 0      tc 0
>             rd 1      ra 0      unused 0  rcode NOERROR       qdcount 1 
>             ancount 0           nscount 0           arcount 1 
>     dns.questions:
>             name www.ibm.com                                                 
>             type A              class IN   
>     dns.additional:
>             name (root)                                                      
>             type 41             class 2048 
>             ttl 32768 (9 hours 6 mins 8 secs)       dlen 0  
> 
> 
> Note the 'dns.additional' section.  Interestingly enough, bind9
> *doesn't always* add the 'additional' section, but it certainly
> appears to add it in the majority of the cases.
> 
> Can anyone explain why the 'additional' section is being added, and
> what purpose it's intended to serve?
> 
> thanks,
> 
> --Chan
> 
>  Chan Wilson :: cwilson at sgi.com :: 650/933-9515 :: SGI Enterprise Net Service
> s
> 
>  People don't ask for facts in making up their minds.  They would rather have
>  one good soul-satisfying emotion than a dozen facts.               --Leavitt
> 
> 
	See RFC 2671:   Extension Mechanisms for DNS (EDNS0)

	8.3 also does EDNS.
--
Mark Andrews, Internet Software Consortium
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark.Andrews at isc.org