Howto:DNS Resolving in SIP
Primary Proxy and Alternative Proxy can be configured.
During initialization (if names - not ip addresses - have been configured):
Both proxy names are resolved by DNS SRV (on no success A query is used).
From the DNS response for primary proxy 2 addresses are selected according to priority and weight values (addr1 and addr2).
From the DNS response for alternative proxy 2 addresses are selected according to priority and weight values (addr3 and addr4).
The SIP signaling interface implements a primary registration and a backup registration.
The primary registration is active all time.
The backup registration is temporarily activated on demand. It is activated if primary registration fails to get registered. And it is deactivated as soon as the primary registration gets registered.
The primary registration tries to register at addr1 exclusively.
The secondary registration tries to register at addr2/addr3/addr4 (round robin).
The DNS information is considered as static.
The primary registration is bound to addr1.
The secondary registration is bound to addr2/addr3/addr4.
No more DNS is done after initialization.
- There's one single exception (v7hotfix4 or later):
In case of no addr2/addr3/addr4 could be retrieved, the secondary registration is not activated, if primary registration fails. A new DNS query is made in order to re-resolve the primary proxy name.