Table 4.2 DNS and ENUM Terminology
Domain Name The Domain Name is a list of labels on the path
from the node to the root of the tree. For example:
ipcom.example.com
is the name of the host ipcomin the example
network registered in the .comtop-level domain
(TLD).
Resource Record (RR) Resource records associated with a particular name,
such as for hosts, mail exchanges, web servers, SIP
servers. For example,
ns.example.com IN A 166.15.21.14
provides the IP address (A) on the Internet (IN) for
the host called nsin the example.comdomain. Or,
mail2.example.com MX example.com
gives the name of the mail server mail2for
example.com. And finally,
SIP3.example.com SIP example.com
refers to a SIP server (Number 3) in the domain
example.com.
A Record (A) An RR that designates a host address. A records are
the most commonly used DNS records for
translating a domain name into an IP address.
Service Record (SRV RR) [12] An RR that contains the locations of servers for a
specific protocol and domain. For example, the
lookup for SIP servers that support the TCP protocol
would be:
_sip._tcp.example.com
The underscore “_” prevents name collisions with
other DNS labels. The response could be:
sip1.example.com
sip2.example.com
sip3.example.com
The response also includes priorities and weights
(not shown here) for the target host, indicating to
the client how to select the target server. Clients can
use a selection mechanism to distribute the load
among servers based on priorities and weights.
(continued)DNS and ENUM 61