[SR-Users] about kamailio.cfg NAT test

[Juha Heinanen]

In kamailio/etc/kamailio.cfg NAT test is based on nat_uac_test("19").
19 includes test 16:

  16 - Test if the source port is different from the port in the “Via”
  header. If the “Via” header contains no port, it uses the default SIP
  port 5060

Based on a couple of tests using baresip, looks like that results in
false positive when UA connects to SIP proxy via TCP.

An example:

T 2020/03/24 13:57:12.685441 192.26.134.10:38940 -> 192.26.134.1:5060 [AP] #127
REGISTER sip:test.tutpro.com SIP/2.0.
Via: SIP/2.0/TCP 192.26.134.10:44717;branch=z9hG4bK5b6aa423104ef942;rport.

Does someone know why test 16 is included?

-- Juha