C.ISI.EDU is a name server for the root, MIL, and EDU domains of the IN class, and would have zones for these domains. The zone data for the root domain might be:
. IN SOA SRI-NIC.ARPA. HOSTMASTER.SRI-NIC.ARPA. ( 870611 ;serial 1800 ;refresh every 30 min 300 ;retry every 5 min 604800 ;expire after a week 86400) ;minimum of a day NS A.ISI.EDU. NS C.ISI.EDU. NS SRI-NIC.ARPA. MIL. 86400 NS SRI-NIC.ARPA. 86400 NS A.ISI.EDU. EDU. 86400 NS SRI-NIC.ARPA. 86400 NS C.ISI.EDU. SRI-NIC.ARPA. A 18.104.22.168 A 10.0.0.51 MX 0 SRI-NIC.ARPA. HINFO DEC-2060 TOPS20 ACC.ARPA. A 22.214.171.124 HINFO PDP-11/70 UNIX MX 10 ACC.ARPA. USC-ISIC.ARPA. CNAME C.ISI.EDU. 126.96.36.199.IN-ADDR.ARPA. PTR SRI-NIC.ARPA. 188.8.131.52.IN-ADDR.ARPA. PTR ACC.ARPA. 184.108.40.206.IN-ADDR.ARPA. PTR SRI-NIC.ARPA. 220.127.116.11.IN-ADDR.ARPA. PTR C.ISI.EDU. 18.104.22.168.IN-ADDR.ARPA. PTR A.ISI.EDU. A.ISI.EDU. 86400 A 22.214.171.124 C.ISI.EDU. 86400 A 10.0.0.52
This data is represented as it would be in a master file. Most RRs are single line entries; the sole exception here is the SOA RR, which uses "(" to start a multi-line RR and ")" to show the end of a multi-line RR. Since the class of all RRs in a zone must be the same, only the first RR in a zone need specify the class. When a name server loads a zone, it forces the TTL of all authoritative RRs to be at least the MINIMUM field of the SOA, here 86400 seconds, or one day. The NS RRs marking delegation of the MIL and EDU domains, together with the glue RRs for the servers host addresses, are not part of the authoritative data in the zone, and hence have explicit TTLs.
Four RRs are attached to the root node: the SOA which describes the root zone and the 3 NS RRs which list the name servers for the root. The data in the SOA RR describes the management of the zone. The zone data is maintained on host SRI-NIC.ARPA, and the responsible party for the zone is HOSTMASTER@SRI-NIC.ARPA. A key item in the SOA is the 86400 second minimum TTL, which means that all authoritative data in the zone has at least that TTL, although higher values may be explicitly specified.
The NS RRs for the MIL and EDU domains mark the boundary between the root zone and the MIL and EDU zones. Note that in this example, the lower zones happen to be supported by name servers which also support the root zone.
The master file for the EDU zone might be stated relative to the origin EDU. The zone data for the EDU domain might be:
EDU. IN SOA SRI-NIC.ARPA. HOSTMASTER.SRI-NIC.ARPA. ( 870729 ;serial 1800 ;refresh every 30 minutes 300 ;retry every 5 minutes 604800 ;expire after a week 86400 ;minimum of a day ) NS SRI-NIC.ARPA. NS C.ISI.EDU. UCI 172800 NS ICS.UCI 172800 NS ROME.UCI ICS.UCI 172800 A 126.96.36.199 ROME.UCI 172800 A 188.8.131.52 ISI 172800 NS VAXA.ISI 172800 NS A.ISI 172800 NS VENERA.ISI.EDU. VAXA.ISI 172800 A 10.2.0.27 172800 A 184.108.40.206 VENERA.ISI.EDU. 172800 A 10.1.0.52 172800 A 220.127.116.11 A.ISI 172800 A 18.104.22.168 UDEL.EDU. 172800 NS LOUIE.UDEL.EDU. 172800 NS UMN-REI-UC.ARPA. LOUIE.UDEL.EDU. 172800 A 10.0.0.96 172800 A 22.214.171.124 YALE.EDU. 172800 NS YALE.ARPA. YALE.EDU. 172800 NS YALE-BULLDOG.ARPA. MIT.EDU. 43200 NS XX.LCS.MIT.EDU. 43200 NS ACHILLES.MIT.EDU. XX.LCS.MIT.EDU. 43200 A 10.0.0.44 ACHILLES.MIT.EDU. 43200 A 126.96.36.199
Note the use of relative names here. The owner name for the ISI.EDU. is stated using a relative name, as are two of the name server RR contents. Relative and absolute domain names may be freely intermixed in a master