I do this with my proxy that fronts freeswitch (https://www.npmjs.com/package/drachtio-fs-load-balancing-proxy <https://www.npmjs.com/package/drachtio-fs-load-balancing-proxy>) by evaluating SIP headers for the common sip scanner signatures and dynamically adding the senders to an iptable black list. This does result in a 100 Trying going back to the sender (since that is sent by my sip stack before proxy processing) but no final response, and every subsequent message from that address is silently dropped.