I have SIP spammers from China trying to crack my OpenWRT( to make free calls using my Asterisk PBX system I guess).
I already lost $10 because of this (my PBX was open to all in these days, so I can't complain much)
But now they are sometimes making my router crash by trying to register with a random username (such as "caller") and trying a lot of passwords. Is there something I can do to block these? Preferably I would not change the port number because the default is convenient.