Why can the sip provider drop our trunk?

Question

SIP

Good day to all!
After changing the ip of our Elastix, the trunk stopped connecting to one of the providers. With other 4 the trunk rose.
Maybe due to the fact that our internal elastix ip is found in the logs? He is behind nat. But our external ip and local network are specified in the configs (without this, the voice did not go for nat).
tcpdump shows during registration an exchange of 4 packets:
1) from us to the provider REGISTER sip: SIP/2.0
2) from the provider SIP/2.0 401 Unauthorized
3) from us REGISTER sip: SIP/2.0
4) from the provider SIP/2.0 403 Forbidden
In logs:
<------------->
--- (11 headers 0 lines) ---
Responding to challenge, registration to domain/host name
REGISTER 11 headers, 0 lines
Reliably Transmitting (NAT) to :5060:
REGISTER sip: SIP/2.0
Via: SIP/2.0/UDP :5060;branch=z9hG4bK06d19161;rport
Max-Forwards: 70
From: @ >;tag=as00d693a5
To: @>
Call-ID : [email protected] <our non-external ip>
CSeq: 103 REGISTER
User-Agent: FPBX-2.8.1(1.8.20.2)
Authorization: Digest username="", realm="asterisk", algorithm=MD5, uri="sip: ", nonce="226127f9", response="9ba46ff2220c5614e83081a657a04096"
Expires: 120
Contact: :5060>
Content-Length: 0
---
<--- SIP read from UDP::5060 --->
SIP/2.0 403 Forbidden
Via : SIP/2.0/UDP <our non-external ip>:5060;branch=z9hG4bK06d19161;received=<our non-external ip>;rport=5060
From: >;tag=as00d693a5
To: >;tag=as17c18a73
Call-ID: [email protected]<our non-external ip >
CSeq
: Asterisk PBX 1.8.28.0
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO, PUBLISH, MESSAGE
Supported: replaces, timer
Content-Length: 0
<---------- --->
--- (10 headers 0 lines) ---
Really destroying SIP dialog '[email protected]<our non-external ip>' Method: REGISTER

Answer 1

Ask your provider. On his Asterisk (ask if they are afraid to provide communication services on non-certified equipment) there should be logs why authorization fails. Most likely, there is a restriction on the registration IP address ("ACL") on the provider's side.

Answer 2

PBX for nat?
General settings - Asterisk settings for SIP ( http://your ext ip/admin/config.php?display=sipsettings)
nat=yes
externip={your external ip}