Thank you for your response. 

I do not have this issue with UDP, it is when I switch to TCP that an INVITE is sending the Unauthorized.

If I attempt something like , the code below, the INVITE is not sent out again (as I thought it would be).  I see the ACK being relayed after the Authentication error, and that is it.

if (t_check_status("401")) {
    if (!auth_check("$fd", "sipusers", "1")) {
              auth_challenge("$fd", "0");
              exit;
    }
} 

I did attempt the uac_auth() as you suggested, but I got no further.

Thanks again!

-----Original Message-----
From: sr-users [mailto:sr-users-bounces@lists.kamailio.org] On Behalf Of Daniel Tryba
Sent: Friday, May 25, 2018 9:47 AM
To: Kamailio (SER) - Users Mailing List <sr-users@lists.kamailio.org>
Subject: Re: [SR-Users] Switching form UDP to TCP causes authentication errors

On Thu, May 24, 2018 at 11:29:54PM +0000, Wilkins, Steve wrote:
> When I switched from UDP to TCP I started getting Authentication
> Errors, Asterisk responds to an INVITE via Kamailio with a '401
> Unauthorized', but Kamailio does nothing with it.

Did you get 401 responses using UDP? Do you have any logic in place to respond to the 401? By default kamailio does nothing.

> Processing just stops near WITH_BLOCK401407.  Shouldn't the 401 be
> relayed so a new INVITE can be sent?

What does "stops near" mean? What does WITH_BLOCK401407 do? The name suggest to block/do nothing with 401 and 407s.

What you need to do is call uac_auth() with the correct credentials to respond to the challenge:
https://www.kamailio.org/docs/modules/stable/modules/uac.html#uac.f.uac_auth

Or is the problem Asterisk challenges INVITEs using TCP?

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