[asterisk-bugs] [JIRA] (ASTERISK-29433) res_rtp_asterisk: Server reflexive candidates use incorrect raddr for RTCP

[Joshua C. Colp (JIRA)]

    [ https://issues.asterisk.org/jira/browse/ASTERISK-29433?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=254920#comment-254920 ] 

Joshua C. Colp edited comment on ASTERISK-29433 at 5/18/21 4:07 AM:
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Severity is severity to the project and the user base as a whole, not to your specific deployment. In this case there are no other reported issues so far with this, if that changes then it can be increased. Additionally severity doesn't generally impact time to resolution except for certain situations so if you're expecting the fact it is Major to alter that, it is unlikely to.


was (Author: jcolp):
Severity is severity to the project and the user base as a whole, not to your specific deployment. In this case there are no other reported issues so far with this, if that changes then it can be increased. Additionally severity doesn't generally impact time to resolution so if you're expecting the fact it is Major to alter that, it is unlikely to.

> res_rtp_asterisk: Server reflexive candidates use incorrect raddr for RTCP
> --------------------------------------------------------------------------
>
>                 Key: ASTERISK-29433
>                 URL: https://issues.asterisk.org/jira/browse/ASTERISK-29433
>             Project: Asterisk
>          Issue Type: Bug
>      Security Level: None
>          Components: Resources/res_rtp_asterisk
>    Affects Versions: 16.17.0, 18.4.0
>            Reporter: Chris
>            Severity: Major
>         Attachments: no_audio_reproduction.zip
>
>
> Frequently our field-testers are complaining about missing audio and video.
> After troubleshooting with the developer of our client SIP stack (AmSip/OSip2) we came to the conclusion that the root-cause is in Asterisk.
> In the cases where no audio (or video) is received, it seems that Asterisk is sending the media packets to the wrong port.
> See our engineer's detailed network analysis below.
> _________________________________
> FIRST OBSERVATION
> _________________________________
> From asterisk_tcpdump.cap
> packet 1243: asterisk (192.168.1.2) makes a STUN BINDING REQUEST from port 14429
> packet 1251: asterisk receive an answer MAPPED-ADDRESS: 78.22.132.194:14429
> This means the packet was received by stun server from the NAT IP 78.22.132.194 AND NAT PORT 14429
> This means the NAT has forwarded the packet **without** changing the PORT. (NAT are often changing port)
> This means the candidate should be:
> a=candidate:S4e1684c2 2 UDP 1694498814 78.22.132.194 14429 typ srflx raddr 192.168.1.2 rport 14429\r\n
> But it appears in SDP as:
> a=candidate:S4e1684c2 2 UDP 1694498814 78.22.132.194 14429 typ srflx raddr 192.168.1.2 rport 14428\r\n
> CONCLUSION: THIS IS AN ERROR FROM ASTERISK
> _________________________________
> SECOND OBSERVATION
> _________________________________
> Let's look at iphone_tcpdump.pcap  "with filter (udp.port == 12600) && (ip.addr == 192.168.1.2)"
> We can see many packets being sent to 192.168.1.2:14428, but nothing received. I guess
> this is expected.
> Let's look at asterisk_tcpdump.pcap  "with filter udp.port == 14428 && ip.addr == 192.168.0.201"
> packet 1529: We can see a a bind request being sent  + a retransmission
> The request is sent FROM 192.168.1.2 from port 14428 to 192.168.0.201on port 12601
> The request TID is :Message Transaction ID: 0e5c00008d4ca0783b1a7b48
> Then, asterisk receive a response:
> packet 1538 is the symmetric response. It contains a XOR-MAPPED-ADDRESS: 192.168.0.145:14428
> This response has been built from amsip.
> This response is coming from 192.168.0.201from PORT 12601
> Let's look  iphone_tcpdump.pcap if we can find this request + answer:
> Let's use the filter "(udp.port == 12601) && (ip.addr == 192.168.0.145 && udp.port == 14428)"
> The packet 721 is matching the request. It's coming on RTCP port (12601) but comes from the RTP port (14428)
> The packet 723 is correct and match the response
> amsip has correct processing: amsip understand this is coming to the RTCP port and establish the RTCP connection.
> Unfortunately, asterisk has sent the packet from port 14428 instead and this is NOT CORRECT.
> ____________________
> FINAL CONCLUSION
> ______________________
> Asterisk has sent packet 1529 from the wrong port.
> The fact that asterisk is using the wrong port (14428) in the RTCP candidate has no impact, but still it's WRONG.
> There was no NAT issue.



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