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DNS

DNS. 12.1 DNS resource records 12.2 The naming authority pointer (NAPTR) DNS RR 12.4 Service records (SRVs). 12.1 DNS resource records. Domain Name Service (DNS)

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DNS

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  1. DNS

  2. 12.1 DNS resource records • 12.2 The naming authority pointer (NAPTR) DNS RR • 12.4 Service records (SRVs)

  3. 12.1 DNS resource records • Domain Name Service (DNS) • a distributed database holding the alphanumeric names and their corresponding IP addresses (and more) of every registered system on a Transmission Control Protocol (TCP)/IP network, such as the Internet or the IP Multimedia Subsystem (IMS) • each entry is referred to as a resource record (RR)

  4. The alphanumeric names (domain names) are hierarchical in nature where country, company, department and even a host (machine) name can be identified • each step in the hierarchy is identified as a zone • The domain name below identifies a machine named pc27 in the engineering department of an Australian company called Foobar pc2 7.engineering.foobar.com.au

  5. An entry in a DNS server that maps a domain name to an IP address is referred to as an address record, or A record • In IPv6 these records are referred to as AAAA records

  6. 12.2 The naming authority pointer (NAPTR) DNS RR • NAPTR RRs are used to replace compact, regular expressions with a replacement field that may well be a pointer to another rule • The DNS-type code for NAPTR is 35 • Table 12.1 describes each field in detail • The format of a NAPTRrecord is as follows Domain TTL Class Type Order Preference Flag Service Regexp Replacement

  7. 12.2.1 NAPTR example • This example uses the SIP service • A NAPTR RR looks like

  8. In this example a client of the SIP service that does not support the Transport Layer Security (TLS) performs a NAPTR RR look-up for the "example.com." domain and selects the replacement _sip._tcp.example.com

  9. 12.4 Service records (SRVs) • An entity must know the exact address of a server to contact for a service • With the introduction of SRV RRs in [RFC2782], DNS clients can query a domain for a service or protocol and get back the names of servers • Administrators can use SRV RRs to distribute the load by using several servers to service a single domain • The DNS-type code for SRVs is 33 • Table 12.2 describes each field in detail

  10. The format of an SRV record is as follows _Service._Proto.Name TTL Class SRV Priority Weight Port Target

  11. 12.4.1 SRV example • Continuing with the example, the SRV RR looks like

  12. In this example the client of the SIP service in the "examp.com" domain performs an SRV look-up of "_sip._tcp.example.com" followed by an A record look-up for server2.example.com

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