Cisco Prime IP Express supports Naming Authority Pointer (NAPTR) RRs.
These records help with name resolution in a particular namespace and are
processed to get to a resolution service. Because NAPTR records are a proposed
standard, RFC 3403, Cisco Prime IP Express only validates their numeric record
fields. However, the proposed standard requires a value for each field, even if
it is null (“”), and there are no preset values.
When using a NAPTR record to locate a Session Initiation Protocol
(SIP) proxy, see the proposed standard, RFC 2916 or RFC 3263. In RFC 2916, the
ENUM working group of the Internet Engineering Task Force specifies NAPTR
records to map E.164 addresses to Universal Resource Identifiers (URIs). Using
the NAPTR record resolves a name in the E.164 international public
telecommunication namespace to a URI, instead of providing the name of a
service to use as a resolver. The U flag was added to the NAPTR record for this
For example, to specify a SIP proxy for the phone number +4689761234,
add a NAPTR record at the name 220.127.116.11.18.104.22.168.6.4.e164.arpa. with this
100 10 "u" "sip+E2U" "/^.*$/sip:firstname.lastname@example.org/" .
This sets these fields of the NAPTR record:
order = 100
preference = 10
flags = "u"
service = "sip+E2U"
regexp = "/^.*$/sip:email@example.com/"
replacement = .
After you configure these fields, the DNS client dealing with phone
number +4689761234 can now find an SIP service URI by replacing the number with
sip:firstname.lastname@example.org. The E.164 zone mostly uses the NAPTR record for wholesale
replacement of the input telephone number. Section 3.2.3 of RFC 2916 includes
an example of one transformation to a Lightweight Directory Access Protocol
(LDAP) query that preserves some of the digits. The E.164 zone does not map to
service location (SRV) records because it wants to obtain a SIP URL that is
more humanly readable to the left of the at (@)