watchNS/cdn.gitbook.comについて、ここに記述してください。
$ dnsq ns cdn.gitbook.com a.gtld-servers.net 2 cdn.gitbook.com: 175 bytes, 1+0+2+4 records, response, noerror query: 2 cdn.gitbook.com authority: gitbook.com 172800 NS hugh.ns.cloudflare.com authority: gitbook.com 172800 NS dahlia.ns.cloudflare.com
$ dnsq ns cdn.gitbook.com a.gtld-servers.net
2 cdn.gitbook.com: 175 bytes, 1+0+2+4 records, response, noerror query: 2 cdn.gitbook.com authority: gitbook.com 172800 NS hugh.ns.cloudflare.com authority: gitbook.com 172800 NS dahlia.ns.cloudflare.com
$ dnsq ns cdn.gitbook.com ns1.gitbook.me
2 cdn.gitbook.com: 64 bytes, 1+1+0+0 records, response, noerror query: 2 cdn.gitbook.com answer: cdn.gitbook.com 3600 A 128.199.158.79
なにを訊いても、Aを返すようだ。
$ dnsq ns qmail.cdn.gitbook.com ns1.gitbook.me 2 qmail.cdn.gitbook.com: 76 bytes, 1+1+0+0 records, response, noerror query: 2 qmail.cdn.gitbook.com answer: qmail.cdn.gitbook.com 3600 A 128.199.158.79