Asterisk Responds with 501 to Keep-Alive


We have a Kamailio server as an edge proxy and mid-registrar behind NAT on the same LAN as the PBX. The phones are remote (behind NAT as well).
When the phone sends a NOTIFY with Event: keep-alive Asterisk responds with a 501 Not Implemented.

See full SIP trace, taken on Kamailio:

I am probably missing something simple…


If you are referring to PJSIP being used, there’s no module which currently implements that functionality so it responds with a 501.

Yes, using PJSIP. So I guess you can only use SIP OPTIONS?

That depends on what exactly is required. Asterisk is still responding to the NOTIFY, so it depends if the remote side cares about the response or not. Otherwise OPTIONS will respond with a response, depending on circumstances. (Authentication required, etc)

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