What it means
Asterisk sends OPTIONS (qualify) to the device or provider and got no answer, so it considers the contact unreachable and stops sending calls there.
Why it happens
- The phone is off or changed its address and has not re-registered.
- NAT on the phone side closed the mapping: the qualify packet cannot get back in.
- A firewall drops OPTIONS, or the provider does not answer OPTIONS at all.
How to fix it
- For phones behind NAT: rewrite_contact=yes, rtp_symmetric=yes, force_rport=yes and a qualify_frequency of 30–60 s to keep NAT open.
- Check the path with the SIP check tool from outside, and the NAT type of the site.
- If the provider ignores OPTIONS, set qualify_frequency=0 on its AOR.
Useful tools
SIP server check · NAT type test
Other Asterisk errors
- Request 'INVITE' from '<sip:…>' failed for '203.0.113.5:5060' - No matching endpoint found
- Request 'REGISTER' from '<sip:101@…>' failed for '198.51.100.7:5060' - Failed to authentic
- Call from 'trunk' (UDP:203.0.113.5:5060) to extension '74951234567' rejected because exten
- No response received from 'sip:sip.provider.com' on registration attempt to 'sip:749512345
- Fatal response '403' received from 'sip:sip.provider.com' on registration attempt to 'sip:
- Retransmission timeout reached on transmission 1a2b3c@203.0.113.5 for seqno 102 (Critical