I branched this question to a new topic. If you are constantly receiving SIP REGISTER messages for phone numbers that are not assigned to you, you may be under a SIP attack. One way to prevent this is the create an access-list (ACL) that allows SIP traffic from your SIP server only. Then you will apply this ACL to the public facing policy-class. For example, if your SIP server had the IP address of 220.127.116.11:
ip access-list extended SIP-SERVER
permit udp host 18.104.22.168 any eq 5060
ip policy-class PUBLIC
allow list SIP-SERVER self
This configuration will only allow uninitiated inbound SIP traffic from the specified SIP server's IP address.
I hope that makes sense, but please to not hesitate to reply to this post with additional questions. I will be happy to help in any way I can.
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