While doing the DNS query through dig utility, sometimes i got Additional records in the results while sometimes not. This is very much normal.
But today i saw something interesting in the output of the dig. While querying for fb.com domain, i got some additional records in the response.
Interesting part is the information displayed along with flags.
There dig utility informs that there are ADDITIONAL: 5 (five additional records) while in the actual output section, it displays only 4 additional responses.
This is not specific to fb.com domain only but i am also getting similar things (mismatch in Additional Section) in other domains too.
`[root@Kansal~]# dig fb.com
; <<>> DiG 9.10.3-P3 <<>> fb.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 34411
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 5
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;fb.com. IN A
;; ANSWER SECTION:
fb.com. 221 IN A 31.13.74.36
;; AUTHORITY SECTION:
fb.com. 735 IN NS b.ns.facebook.com.
fb.com. 735 IN NS a.ns.facebook.com.
;; ADDITIONAL SECTION:
a.ns.facebook.com. 3485 IN A 69.171.239.12
a.ns.facebook.com. 3485 IN AAAA 2a03:2880:fffe:c:face:b00c:0:35
b.ns.facebook.com. 3485 IN A 69.171.255.12
b.ns.facebook.com. 3485 IN AAAA 2a03:2880:ffff:c:face:b00c:0:35
;; Query time: 0 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Thu Oct 20 15:24:59 IST 2016
;; MSG SIZE rcvd: 183
[root@Kansal~]# `
Bind version is 9.10.3
Please explain what i am missing here ?
The fifth RR in the Additional section is the OPT pseudo-RR. Its information is displayed under the OPT PSEUDOSECTION header in your example, rather than among the other RRs, since it's special. You can read all about it in RFC 2671.