1. no_cksum

UDP check sum を付けてこないホスト(Verisign管理のようだ)

    a.root-servers.net.domain 
    b.gtld-servers.net..domain 
    c.gtld-servers.net..domain 
    f.gtld-servers.net..domain 
    g.gtld-servers.net..domain 
    h.gtld-servers.net..domain 
    j.gtld-servers.net..domain 
    m.gtld-servers.net..domain 
    av1.nstld.com.domain 
    av2.nstld.com.domain 
    av3.nstld.com.domain 
    f4.nstld.com.domain 
    ns1.dnsvisa.com.domain 
    ns2.dnsvisa.com.domain 
    y.arin.net.domain 

ns1.dnsvisa.com. 3600 IN A 209.112.113.33

$ dig -x 209.112.113.33

; <<>> DiG 9.9.5-3ubuntu0.8-Ubuntu <<>> -x 209.112.113.33
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 7298
;; flags: qr rd ra; QUERY: 1, ANSWER: 7, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1220
;; QUESTION SECTION:
;33.113.112.209.in-addr.arpa.   IN      PTR

;; ANSWER SECTION:
33.113.112.209.in-addr.arpa. 900 IN     PTR     ns.domainnetwork.se.
33.113.112.209.in-addr.arpa. 900 IN     PTR     a1.verisigndns.com.
33.113.112.209.in-addr.arpa. 900 IN     PTR     sbdns3.cscdns.net.
33.113.112.209.in-addr.arpa. 900 IN     PTR     a4.nstld.com.
33.113.112.209.in-addr.arpa. 900 IN     PTR     ns1.euro909.com.
33.113.112.209.in-addr.arpa. 900 IN     PTR     ns1.dnsvisa.com.
33.113.112.209.in-addr.arpa. 900 IN     PTR     spdns3.cscdns.net.

;; Query time: 214 msec
;; SERVER: 127.0.0.2#53(127.0.0.2)
;; WHEN: Tue May 03 14:54:14 JST 2016
;; MSG SIZE  rcvd: 248