In short, if NAT is detected during REGISTER - then Received is set (it later becomes the D-URI when sending something to that Contact).

https://kamailio.org/docs/modules/stable/modules/nathelper.html#nathelper.p.received_avp

Regards,

On Wed, Nov 25, 2020 at 10:54 AM Daniel Greenwald <dgreenwald@gmail.com> wrote:
On a usrloc record there is an Address field and Received field. The Received field is sometimes not set. What causes it to be not set and what is the difference between the two fields. Sorry if this is a dumb question, I looked at documentation but couldn't find it spelled out. Here is are 2 examples from kamcmd ul.dump:
{
       AoR: utkcf9b6h3@ata.phaxio.com
       Contacts: {
               Contact: {
                       Address: sip:utkc4ff9b6h3@69.78.34.56:4615;transport=tcp
                       Expires: 42
                       Q: -1.000000
                       Call-ID: d1c314305df3d342@192.168.0.3
                       CSeq: 129173
                       User-Agent: OBIHAI/OBi200-3.2.2.5898
                       Received: [not set]
                       Path: [not set]
                       State: CS_NEW
                       Flags: 0
                       CFlags: 0
                       Socket: tcp:10.0.22.254:5060
                       Methods: 7839
                       Ruid: uloc-5fbdd369-491e-4
                       Instance: <urn:uuid:00000000-0000-0000-0000-9cadef62b3da>
                       Reg-Id: 0
                       Server-Id: 0
                       Tcpconn-Id: 58
                       Keepalive: 0
                       Last-Keepalive: 1606317577
                       Last-Modified: 1606317577
               }
       }
}




 Contact: {
                Address: sip:mfjngfd272av@192.168.0.106:5060
                Expires: 30
                Q: -1.000000
                Call-ID: 67413de375b2e76c@192.168.0.106
                CSeq: 146320
                User-Agent: OBIHAI/OBi300-3.2.2.5921
                Received: sip:70.34.56.78:5060
                Path: [not set]
                State: CS_NEW
                Flags: 0
                CFlags: 64
                Socket: udp:10.0.22.254:5060
                Methods: 7839
                Ruid: uloc-5fbdd369-490e-efa3
                Instance: <urn:uuid:00000000-0000-0000-0000-9cadef810877>
                Reg-Id: 0
                Server-Id: 0
                Tcpconn-Id: -1
                Keepalive: 1
                Last-Keepalive: 1606314719
                Last-Modified: 1606314719
            }
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