The autodomain parameter can be set to "yes" or "no". When autodomain is enabled, Asterisk will create a domain with the same name as the host machine. It may also create some other domains based on DNS lookups and known IP addresses. For example, it may create domains based on the values given for the parameters "bindaddr" and "externip". To check the list of domains created by autodomain, go to the Asterisk CLI and type "sip show domains" - look for those with [Automatic] in the column "Set by".