[asterisk-users] Failed to authenticate device 100

[Motty]

Hello, I continued to see this errors in the logs:

[2015-12-02 10:05:57] NOTICE[19949]: chan_sip.c:23277 
handle_request_invite: Failed to authenticate device 
100<sip:100 at xx.xx.xx.xx>;tag=10cdeaf7

how do I guard against this kinds of attacks? Also, to get the IP 
address from where this attack come from I use the following command 
"tcpdump -lni eth0 -f "udp port 5060" is there an easy way to get the 
attacker's IP?

Thanks,
Motty
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