[asterisk-users] ICE Candidate collision on dualstack hosts?

[Joshua C. Colp]

On Wed, Aug 23, 2023 at 4:36 AM Benoît Panizzon <benoit.panizzon at imp.ch>
wrote:

> Hi
>
> I'm attempting to use ICE to be able to present all possible RTP
> transports to peers.
>
> 16.28.0~dfsg-0+deb11u2 (I know it's old, but unfortunately Asterisk was
> removed from debian 'stable' and the version in 'sid' is just broken
> (opus + voicemail don't work anymore).
>
> But I ran into an issue when the peer is running rtpengine:
>
> Asterisk offers:
>
> a=candidate:H9da13901 1 UDP 2130706431 157.161.57.1 13104 typ host
> a=candidate:H1054cffa 1 UDP 2130706431 2001:4060:dead:beef::1 13104 typ
> host
> a=candidate:He9b56028 1 UDP 2130706431 fe80::5054:ff:fea2:9057 13104 typ
> host
> a=candidate:H9da13901 2 UDP 2130706430 157.161.57.1 13105 typ host
> a=candidate:H1054cffa 2 UDP 2130706430 2001:4060:dead:beef::1 13105 typ
> host
> a=candidate:He9b56028 2 UDP 2130706430 fe80::5054:ff:fea2:9057 13105 typ
> host
>
> To me this looks like every candidate is duplicated on port +1
>
> rtpengine complains:
>
> [ice] Priority collision between candidate pairs
> sKy64vK5pY86kc9w:H9da13901:2 and sKy64vK5pY86kc9w:H9da13901:2 - ICE will
> likely fail
>
> And indeed RTP starts on IPv6 as proposed by H1054cffa but as soon as a
> re-invite is processed rtpengine switches to I guess H9da13901 and rtp dies.
>
> Why is asterisk proposing two ports per ip protocol? Is there a way to
> configure this more precisely?
>

They are not strictly duplicated. They are candidates for different
components. One is for RTP, one is for RTCP.

-- 
Joshua C. Colp
Asterisk Project Lead
Sangoma Technologies
Check us out at www.sangoma.com and www.asterisk.org
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