いったん、+traceで親のDNSコンテンツサーバを調べて、
$ dig infra.xyz +trace ; <<>> DiG 9.10.0-P1 <<>> infra.xyz +trace ;; global options: +cmd . 346259 IN NS h.root-servers.net. . 346259 IN NS j.root-servers.net. . 346259 IN NS k.root-servers.net. . 346259 IN NS g.root-servers.net. . 346259 IN NS l.root-servers.net. . 346259 IN NS i.root-servers.net. . 346259 IN NS f.root-servers.net. . 346259 IN NS c.root-servers.net. . 346259 IN NS b.root-servers.net. . 346259 IN NS m.root-servers.net. . 346259 IN NS d.root-servers.net. . 346259 IN NS a.root-servers.net. . 346259 IN NS e.root-servers.net. . 347445 IN RRSIG NS 8 0 518400 20150224050000 20150214040000 16665 . 49XDs9Icoki4ReHy1mUexld6E7w8xCb7NTXMlie4bckAQ2p61KjzkhbJ 89DT98Xpc2IcfJy1TWgee2CTthYXXbLuuhEJdZEUrlJW2ku2IjSaEH3L JlriAwtHgrziIKgWseXAxUVJc7/w+QoYd9XV7oIOHwL3Q8MH65ako+z2 nm8= ;; Received 913 bytes from 127.0.0.1#53(127.0.0.1) in 14 ms xyz. 172800 IN NS z.nic.xyz. xyz. 172800 IN NS y.nic.xyz. xyz. 172800 IN NS x.nic.xyz. xyz. 172800 IN NS generationxyz.nic.xyz. xyz. 86400 IN DS 3599 8 1 3FA3B264F45DB5F38BEDEAF1A88B76AA318C2C7F xyz. 86400 IN DS 3599 8 2 B9733869BC84C86BB59D102BA5DA6B27B2088552332A39DCD54BC4E8 D66B0499 xyz. 86400 IN RRSIG DS 8 1 86400 20150226050000 20150216040000 16665 . 2wVBaGY2zO+b1jX12HPs7Ly0za90q+AtGM5tm3fRyOrDpCQt1XD0iJnc ij2jWuXWWXL8005Qqvi5C/gRiGJswfChKuX4J4/OKGGPzSVjxGynuEQu m3hTUtFWNESuGRAqS1zlsypFRP9O8mpaTamHRxamcQuvDSrbZBLpTbb3 sOU= ;; Received 537 bytes from 192.33.4.12#53(c.root-servers.net) in 122 ms infra.xyz. 3600 IN NS ns1.infra.xyz. infra.xyz. 3600 IN NS ns2.infra.xyz. 1h97h2oec2juov8dlbbjj6i7ik26bm8d.xyz. 3600 IN NSEC3 1 1 1 - 1KKABMBG1LO63FOI21UHUBCQJDM5D2RM NS SOA RRSIG DNSKEY NSEC3PARAM 1h97h2oec2juov8dlbbjj6i7ik26bm8d.xyz. 3600 IN RRSIG NSEC3 8 2 3600 20150311130404 20150209214037 38328 xyz. teRlK0XJ4/Z4SmzTdI3idnwN4Zf4rLHYBap/w0KV34CB6ICtkWsBM1bk hWS4jSQ6XrjFO/OrOEKvgl/DcoyYiEsijJkcqo364JYAVUCzK1cdHlJQ efbZjruxLPEoe+34jb6gZvuY15huradsTnEnyDKQraMuOnLCUpqqiKun L9E= jap3nebfhkg51v8uie6lh8n8fm536euf.xyz. 3600 IN NSEC3 1 1 1 - JTBA28MNE9VHFM3561JQOEB66MS83DLK NS DS RRSIG jap3nebfhkg51v8uie6lh8n8fm536euf.xyz. 3600 IN RRSIG NSEC3 8 2 3600 20150315190829 20150213161936 38328 xyz. ctm4qzSZRJt9gww/VHZ7PhDS8bEkpaRdkSi2FqyIf+hBA83Z7nWvQGUN Ubxd/kgR37gd3NDXoFXiJ3jhYBqJn6Ejfv9kPCv08kjEJ2lQ9W6wfSnA z8Fw67+SvQlwOIntcuDGvW7eL7He5B0C2VmQXVhLhI8dBzpbYR8tMove VCc= ;; Received 591 bytes from 185.24.64.42#53(y.nic.xyz) in 137 ms infra.xyz. 600 IN A 153.121.58.159 infra.xyz. 600 IN NS ns2.infra.xyz. infra.xyz. 600 IN NS ns1.infra.xyz. ;; Received 122 bytes from 153.121.58.159#53(ns1.infra.xyz) in 0 ms
親（z.nic.xyz）に向かって問い合わせると、AUTHORITY SECTIONとADDITIONAL SECTIONにグルーレコードの情報が表示される。
$ dig infra.xyz @z.nic.xyz ; <<>> DiG 9.10.0-P1 <<>> infra.xyz @z.nic.xyz ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 37776 ;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 2, ADDITIONAL: 3 ;; WARNING: recursion requested but not available ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096 ;; QUESTION SECTION: ;infra.xyz. IN A ;; AUTHORITY SECTION: infra.xyz. 3600 IN NS ns1.infra.xyz. infra.xyz. 3600 IN NS ns2.infra.xyz. ;; ADDITIONAL SECTION: ns1.infra.xyz. 3600 IN A 153.121.58.159 ns2.infra.xyz. 3600 IN A 153.121.58.159 ;; Query time: 55 msec ;; SERVER: 2a04:2b00:13ee::42#53(2a04:2b00:13ee::42) ;; WHEN: Mon Feb 16 23:22:27 JST 2015 ;; MSG SIZE rcvd: 106
ちなみに、何も指定せずに普通に問い合わせた時に出るAUTHORITY SECTIONとADDITIONAL SECTIONは、グルーレコードの値ではなく、実際のDNSコンテンツサーバ（今回の例で言えばns1.infra.xyzとns2.infra.xyz）で設定されているNSレコードとAレコードの値なので注意。
