Couple of Doubts on Using Dig

Question

I'm trying to solve some exercises on using Dig and I'm getting allot of doubts.
- When I do: dig +multiline www.twitter.com how do I know if the answer I got came from a authoritative server, is there anyway of knowing this?
- When I repeatedly do: dig +multiline www.twitter.com why does my answer change from time to time?
- When I do: dig -x 31.13.72.65 (or any other IP), in the response it shows "ADDITIONAL:1", why doesnt it show up later on the response?
- I'm trying to do: dig +trace www.lon.ac.uk but it's not showing up any results am I doing something wrong?

Thanks for all your help, hope you can help me :)

Answer 1

You would want to also dig the twitter.com. When getting a reply from the authoritative server (the additional section) you will also get an SOA record.

;; Truncated, retrying in TCP mode.

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.23.rc1.el6_5.1 <<>> @ns3.p34.dynect.net twitter.com -t any
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 5553
;; flags: qr aa rd; QUERY: 1, ANSWER: 23, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;twitter.com.           IN  ANY

;; ANSWER SECTION:
twitter.com.        30  IN  SOA ns1.p26.dynect.net. zone-admin.dyndns.com. 2007116775 3600 600 604800 60