For example, after translating the phone number +1-770-555-1212 into the URI 2.1.2.1.5.5.5.0.7.7.1.e164.arpa as described by E.164 , DDDS is used to transform it using rewrite rules gathered from NAPTR records. The BIND configuration for the records returned from a query for 2.1.2.1.5.5.5.0.7.7.1.e164.arpa might look like:
2.1.2.1.5.5.5.0.7.7.1.e164.arpa.
- $!sip:information@pbx.example.com!i" .
- $!mailto:information@example.com!i" .
- $!sip:information@pbx.example.com!i" is evaluated transforming our original request of 2.1.2.1.5.5.5.0.7.7.1.e164.arpa into sip:information@pbx.example.com. In the regular expression, the exclamation mark '!' will be our delimiter (we avoid the use of '/' and '\' because they may be interpreted as escape sequences somewhere else). The "^.---$" in the RE says "starting at the beginning, including any characters and ending at the end" (in other words, everything) is changed to "sip:information@pbx.example.com" and 'i' ignores case. (Observant readers will notice that the 'i' doesn't matter, given the use of ".---") For those familiar with Perl REs, the equivalent RE could be written as "/^.---$/mailto:information@example.com/i". So the resulting URI "sip:information@pbx.example.com" will be used. If we didn't support SIP, we would effectively fall back to the rule resulting in "mailto:information@example.com".
- RFC 2915 - was previously the specification for NAPTR (superseded by RFC 3403 below)
- RFC 3401 - DDDS (Dynamic Delegation Discovery System) - uses NAPTR records
- RFC 3403 - DDDS Part 3 (DNS) now specifies and describes NAPTR records
- Additional background on NAPTR in the context of ENUM can be found at the NIC.at site http://enum.nic.at/documents/Diverse/Background_to_NAPTR.html
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