SIP registrations and issues 401 vs 200

Dear All,

currently I am working on a case with some strange behaviour of SIP-authentication.

I used WireShark in order to see what is happening when one of my phones is trying to register with our PBX. I see that the SIP-authentication is trying to REGISTER but gives twice a 401 (same Cseq-number). Immediatly after the double 401 it is trying the same but with a 200 on the second time (normal behaviour).

Do you have any idea on the double 401 at the first time it is trying to REGISTER?

Again it is not the same attempt due to the difference in the Cseq-number.

Looking forward to your ideas.

401 means there is either no authentication data in the request, or the nonce value is stale. There should be a detailed log message for the latter, if you turn up the logging sufficiently.