watchNS/xw.qmail.jp/b.ns.xw.qmail.jpについて、ここに記述してください。
$ dig a b.ns.xw.qmail.jp @127.0.0.2
; <<>> DiG 9.9.5-3ubuntu0.5-Ubuntu <<>> a b.ns.xw.qmail.jp @127.0.0.2 ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 37277 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096 ;; QUESTION SECTION: ;b.ns.xw.qmail.jp. IN A ;; ANSWER SECTION: b.ns.xw.qmail.jp. 300 IN A 14.192.44.29 ;; Query time: 39 msec ;; SERVER: 127.0.0.2#53(127.0.0.2) ;; WHEN: Fri Dec 11 10:44:52 JST 2015 ;; MSG SIZE rcvd: 61
[1449798292] unbound[1072:0] info: resolving b.ns.xw.qmail.jp. A IN [1449798292] unbound[1072:0] info: response for b.ns.xw.qmail.jp. A IN [1449798292] unbound[1072:0] info: reply from <qmail.jp.> 14.192.44.5#53 [1449798292] unbound[1072:0] info: query response was REFERRAL [1449798292] unbound[1072:0] info: resolving xw.qmail.jp. NS IN [1449798292] unbound[1072:0] info: resolving xw.qmail.jp. NS IN [1449798292] unbound[1072:0] info: response for b.ns.xw.qmail.jp. A IN [1449798292] unbound[1072:0] info: reply from <xw.qmail.jp.> 14.192.44.29#53 [1449798292] unbound[1072:0] info: query response was NXDOMAIN ANSWER [1449798292] unbound[1072:0] info: response for b.ns.xw.qmail.jp. A IN [1449798292] unbound[1072:0] info: reply from <xw.qmail.jp.> 14.192.44.29#53 [1449798292] unbound[1072:0] info: query response was ANSWER