Enum Dialing; Configuring Enum; Configuring Dns Naptr Records - TANDBERG Gatekeeper User Manual

TANDBERG Gatekeeper User Manual

8 ENUM dialing

ENUM provides another DNS based dialing scheme. Users dial an E.164 number — a telephone
number — which is converted in to an H.323 URI by the DNS system. The rules for URI dialing
are then followed to place the call. This allows you to retain the flexibility of URI dialing whilst
having the simplicity of calling using just a number.
Before the DNS lookup can be performed, the E.164 number must be transformed into a host
name. To do this, the digits are reversed and separated by a dot — similar to the way DNS PTR
records are formed. The DNS zone is then appended. If an ENUM root of e164.example.com
is being used, and the dialled number is +47 67 125 125, then the transformed host name is
5.2.1.5.2.1.7.6.7.4.e164.example.com
RFC 3761, which defines the ENUM standard specifies that the DNS zone for ENUM is
e164.arpa. Use of this DNS zone requires that your E.164 numbers are assigned by an
appropriate national regulatory body. Not all countries are yet participating in ENUM, so it may
be useful to use an alternative DNS zone for ENUM. This could either be within your corporate
DNS zone or could use a public ENUM database such as http://www.e164.org
The DNS zone used for ENUM contains NAPTR records as defined by RFC 2915. These provide
the mapping between E.164 numbers and H.323 URIs.
The Gatekeeper may be configured with up to 5 DNS zones to search for a NAPTR record. It will
iterate through them in order, stopping when the first record is found.
8.1 Configuring ENUM
ENUM support is disabled by default. In order to enable ENUM support on your Gatekeeper,
enter the command:
xConfiguration Gatekeeper ENUM Mode: On
You are provided by default with the global ENUM DNS zone: e164.arpa. If you wish to change
this, or add other DNS zones, enter the command:
xConfiguration Gatekeeper ENUM DNSSuffix [1..5 ]: <zone name>
The ENUM mode and zone may also be set using the web page Gatekeeper Configuration
Gatekeeper shown in figure 19.
If you have a number of Gatekeepers and Border Controllers neighbored together, it is recom-
mended that ENUM support is enabled on only one of them. If ENUM is enabled on more than
one system, call set up could become unpredictable.
8.2 Configuring DNS NAPTR Records
ENUM relies on the presence of NAPTR records, as defined by RFC 2915. This is used to obtain
an H.323 URI from the E.164 number. The record format that the Gatekeeper supports is:
31