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

[Chan Wilson]

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 Services

 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