Unidentified not logged Mass Incoming calls to Extension

Recently one of our extensions gets mass incoming calls supposedly from “100” (nonexistent extension). Those calls are not logged in the CDR nor can I identify the source ip, so I can’t block it and it is rather annoying. Anonymous SIP calls and guest calls are blocked.

Any idea what could be done to block it?

Presumably the calls are direct to the phone without Asterisk being involved, so use a firewall well written or easier, just don’t accept SIP requests on port 5060.

The remote extension is on a remote network for which I have no control…is there anything else I can do?

Nothing you can do , you would have to ask the person with such control over the router or the phone.