AASTRA 6700i series, 9143, 9480i, 9480i CT SIP Administrator Guide EN - Manual (Page 682)

41-001343-01 Rev 03, Release 3.2.2 6-55
Domain Name Server (DNS) Pre-caching Support
The IP phones now support the use of a local DNS host file to resolve DNS queries, and supports
pre-provisioning of DNS SRV records. This feature allows administrators to configure the phone
to download a text file which contains persistent DNS “A record” hostname to IP address
mappings. In addition, support for persistent DNS “SRV records” has been added to permit SRV
based high availability of services.
There are two methods used to configure DNS pre-caching on the IP phone:
• Configure a unix style “host” file used instead of a DNS “A query” to resolve hostnames to IP
addresses. The host file is downloaded and cached on the IP phone.
• Configure DNS “SRV queries” for geographic redundancy and failover. The configured SRV
entries are used to pre-load the DNS cache on the IP phone.
Both these methods are configurable using the configuration files only, and are primarily intended
for use when a third party hosting provider delivers SIP services but does not have local access or
control of the LAN side DNS infrastructure.
Configuring DNS “Host File” Pre-caching from the Configuration Server
The DNS host file must reside on the same server as the configuration files
(aastra.cfg/.tuz, etc.) and the filename to download is specified within the configuration.
Use the following parameter to configure the phone to use the host file for host IP address lookups.
The following procedure is an example of how to use the “sip dns host file” parameter to configure
DNS lookup pre-caching from the configuration server.
Note: Time-to-Live (TTL) used in this feature is hard-coded for each
server and not configurable.
Configuration Files
For the specific parameter you can set in the configuration files, see Appendix A, the section, “DNS Host
File” on page A-250.
Configuring “DNS Host” Pre-caching
1 Using a text-based editing application, create a blank text file
2 Enter the IP addresses of the DNS servers in your local network. For example:
1.2.3.4 server1
5.6.7.8 server2
9.0.1.2 server3
Note: Ensure each line uses a Carriage Return (CR) or Carriage Return + Line Feed (CRLF) to
terminate the line.