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TANDBERG Gatekeeper User Guide
Page 43 of 105
9.4. DNS Records
URI dialing relies on the presence of records in the DNS information for the zone. For preference service
(SRV) records should be used. These specify the location of a server for a particular protocol and
domain. Their format is defined by an Internet standard (RFC 2782 [3]) as
_Service._Proto.Name TTL Class SRV Priority Weight Port Target
The Gatekeeper supports two types of SVR record as defined by H.323 Annex O. These are Location and
Call, with _Service set to _h323ls and _h323cs respectively.
For URI dialing on a Gatekeeper _Service is defined by the H.323 protocol suite to be _h323ls and
_Proto is _udp. Name corresponds to the host part of the H.323 URI.
Process
When the Gatekeeper receives a request to call fred@example.com, it will first search all the zones it
knows about for that alias. If it can not be located, the Gatekeeper will then attempt to locate the
destination using the DNS system, as follows:
1. First the Gatekeeper will query for a Location SRV record, to discover the authoritative
Gatekeeper for the destination DNS zone.
2. If is not located, the Gatekeeper will query for a Call SRV record and try to place the call to that
address.
3. If no appropriate SRV record can be located, the Gatekeeper will fall back to looking for an A or
AAAA record for the domain. If a record is found, a call will be placed to that address.
If you intend to use URI dialing, you should provide at least a Location SRV record: it provides the most
flexibility and the simplest configuration. Call SRV records and A/AAAA records are intended primarily for
use by endpoints which cannot participate in a location transaction, exchanging LRQ and LCF.
Example configuration
Configuration of a system for a company with the domain name example.com might typically be:
A record for box.example.com returns the IP address of the box
SRV record for _h323ls._udp.example.com returns box.example.com
SRV record for _h323cs._tcp.example.com returns box.example.com
System name set to box.example.com
LocalDomain DomainName set to example.com
How you add the DNS records depends on the type of DNS server you are using. Instructions for setting
up two common DNS servers are given in Appendix A.