[SR-Users] How ICE works with private IPs as candidates?

[Denys Pozniak]

Hello!

I have next topology: ISP->Kamailio + Rtpengine->WebRTC
Sometimes I receive from Browser side SDP like below with private IPs in
ICE candidates.

   - Please explain why it happens?
   - How ICE finds a pair? I think Rtpengine obtains packet from Browser
   and somehow matches with peer (as it can't reach Browser via private IP)



U KAMAILIO_IP:34150 -> RTPENGINE_IP:22222
0_16586_545 d3:sdp962:v=0.
o=- 3981552194926701250 2 IN IP4 127.0.0.1.
s=-.
t=0 0.
a=msid-semantic: WMS 5efe361e-087d-47de-98f6-9b51427d3764.
m=audio 50589 RTP/SAVPF 8 0.
c=IN IP4 192.168.2.205.
a=rtcp:9 IN IP4 0.0.0.0.
a=candidate:710145796 1 udp 2122255103 <(212)%20225-5103>
2001::9d38:6abd:3c21:28f:3f57:fd32 50588 typ host generation 0 network-id 1
network-cost 50.
a=candidate:2355154215 1 udp 2122194687 <(212)%20219-4687> 192.168.2.205
50589 typ host generation 0 network-id 2.
a=ice-ufrag:sPAh.
a=ice-pwd:RjXqOz8rpwjhKPU3BzXkJd1d.
a=fingerprint:sha-256 04:AF:D4:6C:07:C2:DD:18:48:E0:
BC:46:15:15:00:5F:C9:AD:CF:8D:F3:94:55:5A:54:0C:37:B3:E6:44:63:EC.
a=setup:active.
a=mid:audio.
a=sendrecv.
a=rtcp-mux.
a=rtpmap:8 PCMA/8000.
a=rtpmap:0 PCMU/8000.
a=ssrc:3055599516 <(305)%20559-9516> cname:n0Cdw7SNbYDIba8s.
a=ssrc:3055599516 <(305)%20559-9516> msid:5efe361e-087d-47de-98f6-9b51427d3764
41750b25-d640-4bad-8953-55f4e2684c49.
a=ssrc:3055599516 <(305)%20559-9516> mslabel:5efe361e-087d-47de-
98f6-9b51427d3764.
a=ssrc:3055599516 <(305)%20559-9516> label:41750b25-d640-4bad-8953-
55f4e2684c49.
3:ICE6:remove5:flagsl13:trust-address14:media-handover8:
SDES-offe7:replacel6:origin18:session-connectione18:
transport-protocol7:RTP/AVP8:rtcp-muxl5:offer6:accepte7:
call-id37:domain.com_29465313:received-froml3:IP412:10.23.
255.93e8:from-tag13:QQcg5eFv08S9K6:to-tag10:nsebpmf7ia7:command6:answere
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