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

Roman Shpount <roman@telurix.com> Wed, 06 February 2019 01:03 UTC

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From: Roman Shpount <roman@telurix.com>
Date: Tue, 5 Feb 2019 20:03:38 -0500
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To: Justin Uberti <juberti@google.com>
Cc: Alan Ford <alan.ford@gmail.com>, Simon Perreault <sperreault@jive.com>, RTCWeb IETF <rtcweb@ietf.org>, mmusic WG <mmusic@ietf.org>, Christer Holmberg <christer.holmberg@ericsson.com>
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Subject: Re: [MMUSIC] [rtcweb] What goes into c= line address when FQDN is used for the default candidate?
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On Tue, Feb 5, 2019 at 7:57 PM Justin Uberti <juberti@google.com> wrote:

>
> On Tue, Feb 5, 2019 at 10:19 AM Roman Shpount <roman@telurix.com> wrote:
>
>> On Tue, Feb 5, 2019 at 10:03 AM Alan Ford <alan.ford@gmail.com> wrote:
>>
>>> 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.
>>>
>>
>> This is obviously not going to work. At the very minimum ICE client
>> should be listening for connectivity checks on all addresses to which FQDN
>> candidate resolves, including IPv4 and IPv6. It also should do connectivity
>> checks to all addresses. Otherwise, if you have two clients, one dual stack
>> and another single stack, they are not going to see each other, since one
>> will be listening and sending connectivity checks via IPv6 and another via
>> IPv4. This is why language about FQDN was removed from mmusic-ice-sip-sdp
>> -- it was broken.
>>
>
>> For ICE to work, you want to include all possible addresses for FQDN in
>> the candidate list and then proceed with nomination as if they were
>> independent candidates.
>>
>
> I don't think this is correct behavior, but it's really beside the point
> since we can ignore it if we have the one-FQDN-per-address concept we
> discussed.
>

I am not sure why this is wrong, but I agree this is besides the point if
we agree on one-FQDN-per-address. If we agree on one-FQDN-per-address,
rtcweb-mdns-ice-candidates needs to be modified to match. Behavior
currently described there (each sides picks an address in random) is
definitely wrong.

Regards,
_____________
Roman Shpount