Advanced Operational Features
41-001343-02 REV05 – 07.2014 6-37
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 down-
load 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-cach-
ing from the configuration server.
Configuring “DNS Host” Pre-caching
Configuring DNS “Service (SRV) Records” Pre-caching
In addition to using a host file to resolve host names to IP addresses, an Administrator can also configure DNS “SRV
records” (Service Records) for geographic redundancy and failover between application servers in the network.
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 pageA-218.
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.
3. Save the file as “<filename>.txt”. Fo r e x a m p l e , “ hostfile.txt”.
4. Using a text-based editing application, open the aastra.cfg file for the phone(s) for which you want to apply the DNS hostfile.
5. Enter the following parameter in the aastra.cfg file followed by the host file name as the value:
sip dns host file: <filename>.txt
For example:
sip dns host file: hostfile.txt
Note:
If using a text file on a PC to enter this value, you must enter a carriage return (CR) after entering the host file name.
6. Save the file. Make sure the aastra.cfg and the hostfile.txt files are on the configuration server in your network before downloading to the
phone(s).
7. Restart the phone(s) in your network.
The phone(s) downloads the specified host text file and stores it locally on the phone’s flash memory. Upon each subsequent boot of the
phones, if the host text file is available on the configuration server, it is downloaded to replace the locally cached copy; otherwise, the pre-
viously cached copy is retained and used unchanged.
The configuration of the phone(s) can now use server1, server2, or server3 for SIP or other services instead of using the IP addresses. The
phones will continue resolving the host names even if DNS on the network has conflicting or missing entries for server1, server2, or server3,
or if the local LAN DNS server fails to respond.
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