Re: [rtcweb] [MMUSIC] What goes into c= line address when FQDN is used for the default candidate?

Harald Alvestrand <harald@alvestrand.no> Thu, 07 February 2019 16:01 UTC

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From: Harald Alvestrand <harald@alvestrand.no>
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Date: Thu, 7 Feb 2019 17:01:16 +0100
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Subject: Re: [rtcweb] [MMUSIC] What goes into c= line address when FQDN is used for the default candidate?
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Den 05.02.2019 16:03, skrev Alan Ford:
> If that update was to be made, this goes against the text
> in draft-ietf-rtcweb-mdns-ice-candidates-02 which says:
> 
>    An ICE agent that supports mDNS candidates MUST support the situation
>    where the hostname resolution results in more than one IP address.
>    In this case, the ICE agent MUST take exactly one of the resolved IP
>    addresses and ignore the others.  The ICE agent SHOULD, if available,
>    use the first IPv6 address resolved, otherwise the first IPv4
>    address.
> 
> But there’s a bigger problem here, which is how to cope with an FQDN is
> not resolvable. So the intention, as I understand it, is that when these
> host candidates leave the mDNS domain and are thus not resolvable, they
> will be treated as peer reflexive candidates.
> 
> But at that point there is no address family information available, so
> how does an ICE agent know to do pairing with these candidates, which
> requires the address family to be known?

Peer reflective candidates are identified by means of an incoming packet.
The address family is very obvious from the packet.