strange iptables log entry

[M.W. Chang]

My firewall logged this IP trying to access port 68. What is 
prisoner.iana.org? It seems that it doesn't exist at all.

toylet at server: > dig -x 192.168.128.6

; <<>> DiG 9.2.3 <<>> -x 192.168.128.6
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 57716
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0

;; QUESTION SECTION:
;6.128.168.192.in-addr.arpa.    IN      PTR

;; AUTHORITY SECTION:
168.192.in-addr.arpa.   10705   IN      SOA     prisoner.iana.org. 
hostmaster.root-servers.org. 2002040800 1800 900 604800 604800

-- 
   .~.    http://toylet.homeip.net
  / v \   Linux 2.4.22-xfs
/( _ )\  10:00pm up 2 days 1:39
   ^ ^    load average: 0.99 0.97 0.96