DNS and how it affects SIP URI Addressing
From SIPfoundry sipXecs IP PBX, The Open Source SIP PBX for Linux - Calivia
Contents |
Introduction
There are fundamentally two different ways how the sipX system addresses users based on SIP addresses (SIP URIs):
Fully Qualified Hostname (FQHN)
You can use the Fully Qualified Hostname (FQHN) of the sipX server as part of the SIP address (SIP URI). If the name of your sipx server is sipx.domain.com, then a SIP address for a user (or line) on your system would look as follows:
sip:joe@sipx.domain.com sip:200@sipx.domain.com
Your DNS server will need an entry (A record) for the host sipx in order to be able to resolve the fully qualified name. If done right, you should be able to ping your sipx host:
ping sipx.domain.com
Please refer to the install documentation on how to setup and test DNS.
Using DNS SRV Records
As an alternative you can use DNS service records (DNS SRV). Such service records allow a host (or phone) on your network to query the DNS server for the host responsible to handle SIP signaling. The DNS server will then return the fully qualified name of your sipx server (sipx.domain.com). A SIP address for a user (or line) on your system would then look as follows:
sip:joe@domain.com sip:200@domain.com
Please refer to the install documentation on how to setup and test DNS SRV records. The advantage of this approach is clear: A user does not have to know the host name of your sipX server in order to compile an address. The domain name is sufficient.
Note: Using DNS SRV records is typically the preferred approach for an enterprise deployment. This allows SIP addresses to be identical to email addresses.
Configuration of the Domain Name in sipX
The default setting after installation of the sipX system is to use the FQHN. I.e. do not require DNS SRV records to be present in the DNS server for the sipX host. This simplifies installation and removes DNS SRV configuration as one of the most frequently encountered problems installing a sipX system.
This default setting can be changed after installation if you want to use DNS SRV. Go to Configuration and then Domain:
The default setting in the field should represent the FQHN of your sipX server. In order to switch to using DNS SRV instead, change this setting to only be the domain name. After changing this setting, you are informed that services need to restart to make this change effective. This will only take a second or two.
| Important note: Changing this setting affects all the different phones and their lines. It is therefore recommended to change this setting before defining any users and devices. If you encounter problems with certain phones after the change to DNS SRV you might want to check the SIP Registrar (or SIP Server) settings for the different phones. |
| Important note: All profiles for phones need to be resent to proliferate this change to the phones. All phones then have to restart. |
