### Description

The force_socket parameter is not always used when set. If I understand the module documentation correctly, when setting the force_socket parameter, then all nathelper udp traffic will be forced to use this socket definition.

The issue here is a result of another issue first described [here](http://sip-router.1086192.n5.nabble.com/NatHelper-ignoring-force-socket-modu...) in 2015 but is still present in current stable kamailio v5.0.4.

We have 3 registrars running in "memory only" mode, using dmq_usrloc to replicate registrations to the remaining two nodes. On the remaining two nodes there is no socket parameter set for the AOR, but nathelper still wants to ping these AOR's. It is on these two systems where this issue exhibits itself. I will open another ticket for this scenario and try to reference it here as they are related.

Each registrar has two interfaces, one is our "admin" lan, the other is our "voice" lan. The default route is set on these hosts and is a gateway on our "admin" lan. See issue #1297

When the registrars that are replicated to receive the AOR, they attempt to ping the endpoint (ideally they should not ping them). nathelper seems to think that the best interface to send them over is the "admin" lan even though force_socket is defined.

I would have expected that the message should have been sent via the socket defined in the "force_socket" parameter.

### Troubleshooting Module definitions

registrar ``` modparam("registrar", "method_filtering", 1) modparam("registrar", "case_sensitive", 1) modparam("registrar", "append_branches", 0) modparam("registrar", "use_path", 1) modparam("registrar", "path_mode", 0) modparam("registrar", "path_use_received", 1) modparam("registrar", "path_check_local", 1) modparam("registrar", "max_contacts", 1) ```

usrloc ``` modparam("usrloc", "db_mode", 0) modparam("usrloc", "use_domain", 1) modparam("usrloc", "timer_interval", 60) modparam("usrloc", "timer_procs", 4) modparam("usrloc", "nat_bflag", 6) ```

nathelper ``` modparam("nathelper", "natping_interval", 20) modparam("nathelper", "natping_processes", 4) modparam("nathelper", "ping_nated_only", 0) modparam("nathelper", "sipping_from", "sip:keepalive@example.com") modparam("nathelper", "sipping_method", "OPTIONS") modparam("nathelper", "sipping_bflag", 6) modparam("nathelper", "force_socket", "10.7.0.189:5060") modparam("nathelper", "udpping_from_path", 1) ```

Kamailio is listening on the same socket that is defined for the "force_socket" parameter above ``` listen=udp:10.6.0.189:5060 listen=udp:10.7.0.189:5060 listen=tcp:10.6.0.189:80 ```

dmq ``` modparam("dmq", "server_address", DMQ_ADDRESS) modparam("dmq", "notification_address", DMQ_NOTIFY_ADDRESS) modparam("dmq", "multi_notify", 1) modparam("dmq", "num_workers", 4) ```

dmq_usrloc ``` modparam("dmq_usrloc", "enable", 1) ``` #### Reproduction

Using the above settings register a user and once they are replicated to the registrar that did not service the request, the options pings on the nodes that were replicated to will exhibit this issue.

Example AOR where the registration was serviced (options pings should come from this host, and do, and flow as expected) ``` { "jsonrpc": "2.0", "result": { "Domain": "location", "Size": 1024, "AoRs": [{ "Info": { "AoR": "example_user@example.com", "HashID": -1389656423, "Contacts": [{ "Contact": { "Address": "sip:example_user@212.2.172.228:39808;rinstance=ed8aa63e90f53e97;transport=UDP", "Expires": 66, "Q": -1, "Call-ID": "wE-GD4GzkrtuDAJUBJf1Jg..", "CSeq": 58, "User-Agent": "Z 3.15.40006 rv2.8.20", "Received": "sip:212.2.172.228:39808", "Path": "sip:10.7.0.186:5062;lr;received=sip:212.2.172.228:39808", "State": "CS_NEW", "Flags": 0, "CFlags": 64, "Socket": "udp:10.7.0.190:5060", "Methods": -1, "Ruid": "uloc-2-59fa1f9d-714-17", "Instance": "[not set]", "Reg-Id": 0, "Last-Keepalive": 1509615136, "Last-Modified": 1509615136 } }] } } ], "Stats": { "Records": 1, "Max-Slots": 1 } }, "id": 4836 } ```

example AOR of the above registration on a registrar that was replicated to by dmq/dmq_usrloc, ideally these AOR's should not be pinged at all, but, currently they do, but, in this case, when they do get ping'd, they do not use the socket as defined in the "force_socket" parameter. ``` { "jsonrpc": "2.0", "result": { "Domain": "location", "Size": 1024, "AoRs": [{ "Info": { "AoR": "example_user@example.com", "HashID": -1389656423, "Contacts": [{ "Contact": { "Address": "sip:example_user@212.2.172.228:39808;rinstance=ed8aa63e90f53e97;transport=UDP", "Expires": 69, "Q": -1, "Call-ID": "wE-GD4GzkrtuDAJUBJf1Jg..", "CSeq": 91, "User-Agent": "Z 3.15.40006 rv2.8.20", "Received": "sip:212.2.172.228:39808", "Path": "sip:10.7.0.186:5062;lr;received=sip:212.2.172.228:39808", "State": "CS_NEW", "Flags": 2, "CFlags": 64, "Socket": "[not set]", "Methods": -1, "Ruid": "uloc-2-59fa1f9d-714-17", "Instance": "[not set]", "Reg-Id": 0, "Last-Keepalive": 1509617664, "Last-Modified": 1509617664 } }] } } ], "Stats": { "Records": 1, "Max-Slots": 1 } }, "id": 4571 } ```

#### Log Messages

There are no apparent error messages in the logs relating to this that I can see.

#### SIP Traffic

Here you can clearly see that the OPTIONS message is being sent over the "10.6.0.189" interface when the modules "force_socket" parameter is set to "10.7.0.189:5060" ``` U 2017/11/02 08:37:59.426608 10.6.0.189:5060 -> 10.7.0.186:5062

OPTIONS sip:example_user@212.2.172.228:39808;rinstance=ed8aa63e90f53e97;transport=UDP SIP/2.0. Via: SIP/2.0/UDP 10.6.0.189:5060;branch=z9hG4bK8416926. Route: sip:10.7.0.186:5062;lr;received=sip:212.2.172.228:39808. From: sip:keepalive@example.com;tag=uloc-2-59fa1f9d-714-17-9968b2da-13812ff4. To: sip:example_user@212.2.172.228:39808;rinstance=ed8aa63e90f53e97;transport=UDP. Call-ID: c0cec5f7-555ac383-68bb313@10.6.0.189. CSeq: 1 OPTIONS. Content-Length: 0. .

U 2017/11/02 08:38:19.431937 10.6.0.189:5060 -> 10.7.0.186:5062

OPTIONS sip:example_user@212.2.172.228:39808;rinstance=ed8aa63e90f53e97;transport=UDP SIP/2.0. Via: SIP/2.0/UDP 10.6.0.189:5060;branch=z9hG4bK8345318. Route: sip:10.7.0.186:5062;lr;received=sip:212.2.172.228:39808. From: sip:keepalive@example.com;tag=uloc-2-59fa1f9d-714-17-9968b2da-23812ff4. To: sip:example_user@212.2.172.228:39808;rinstance=ed8aa63e90f53e97;transport=UDP. Call-ID: c0cec5f7-655ac383-a9bb313@10.6.0.189. CSeq: 1 OPTIONS. Content-Length: 0. . ```

### Possible Solutions

Unknown

### Additional Information

* **Kamailio Version** - output of `kamailio -v`

``` version: kamailio 5.0.4 (x86_64/linux) flags: STATS: Off, USE_TCP, USE_TLS, USE_SCTP, TLS_HOOKS, USE_RAW_SOCKS, DISABLE_NAGLE, USE_MCAST, DNS_IP_HACK, SHM_MEM, SHM_MMAP, PKG_MALLOC, Q_MALLOC, F_MALLOC, TLSF_MALLOC, DBG_SR_MEMORY, USE_FUTEX, FAST_LOCK-ADAPTIVE_WAIT, USE_DNS_CACHE, USE_DNS_FAILOVER, USE_NAPTR, USE_DST_BLACKLIST, HAVE_RESOLV_RES ADAPTIVE_WAIT_LOOPS=1024, MAX_RECV_BUFFER_SIZE 262144, MAX_LISTEN 16, MAX_URI_SIZE 1024, BUF_SIZE 65535, DEFAULT PKG_SIZE 8MB poll method support: poll, epoll_lt, epoll_et, sigio_rt, select. id: unknown compiled on 10:57:22 Oct 26 2017 with gcc 4.8.5 ```

* **Operating System**: ``` CentOS Linux release 7.4.1708 (Core) Linux localhost 3.10.0-693.5.2.el7.x86_64 #1 SMP Fri Oct 20 20:32:50 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux ```