CHECKSIPDOMAIN()

CHECKSIPDOMAIN(domain)

Checks to see if the specified SIP domain name (may also be an IP address) is local (see sip.conf). Returns the domain name, IP address or empty string.

exten => 123,1,Set(foo=${CHECKSIPDOMAIN(123.45.67.89)})
[Note]

Internal help for this application in Asterisk 1.4: 

  -= Info about function 'CHECKSIPDOMAIN' =- 

[Syntax]
CHECKSIPDOMAIN(<domain|IP>)

[Synopsis]
Checks if domain is a local domain

[Description]
This function checks if the domain in the argument is configured
as a local SIP domain that this Asterisk server is configured to handle.
Returns the domain name if it is locally handled, otherwise an empty str
ing.
Check the domain= configuration in sip.conf

diff output to internal help in Asterisk 1.2: 

- none -