Re: [rtcweb] Is rtcweb the right place for draft-ietf-rtcweb-mdns-ice-candidates?

Justin Uberti <> Thu, 04 July 2019 04:33 UTC

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From: Justin Uberti <>
Date: Wed, 3 Jul 2019 21:33:19 -0700
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To: Roman Shpount <>
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Subject: Re: [rtcweb] Is rtcweb the right place for draft-ietf-rtcweb-mdns-ice-candidates?
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On Wed, Jul 3, 2019 at 6:15 PM Roman Shpount <> wrote:

> This direction was taken since mmusic got no feedback regarding the
> specifics of FQDN support. I did try to get mdns authors, including you, to
> participate in the discussion, since I was afraid this can be a problem,
> but no one responded at that time.

Sorry, I haven't been reading mmusic regularly lately and missed your

> As it stands, there are significant issues with just putting FQDN in
> candidate. The gist of the issue is that due to things like DNS64 there is
> no way to enforce that FQDN will resolve to the same address family to
> which FQDN was originally pointed to. So, end points will end up either
> with different address families or with multiple addresses for the same
> candidate even when FQDN in candidate originally only pointed to a single
> IP. Connectivity checks will likely succeed on some of those address pairs,
> but figuring out priority for the candidate pairs becomes confusing and
> under-specified. No one wanted to discuss or deal with this before
> ice-sip-sdp was published so the current language was put in place.

I need to understand the DNS64 issue better, I'm not sure how this would
pose a problem in practice.

> I know the browsers are trying to address what they perceive is a
> significant issue, but I would think that current mdns draft is fairly raw
> and turning this option on is likely premature. It might lead to multiple,
> non-backwards compatible versions of this feature.

If anything, I think we've been too slow here. The initial mDNS draft was
posted over a year ago.

> On Wed, Jul 3, 2019 at 8:58 PM Justin Uberti <> wrote:
>> Hmm, that's unfortunate. I think this is a mistake, given that we are
>> about to throw the switch to enable mDNS for 100% of Chrome endpoints;
>> Chrome (and soon all browsers) will have to ignore ice-sip-sdp until this
>> extension spec is written.
>> ice-sip-sdp isn't published yet, so it seems an update to that document
>> could still be a possibility. If that's not an option, putting forth #1 as
>> a specific extension that allows FQDN candidates to be generated in certain
>> situations seems like the right path.
>> On Wed, Jul 3, 2019 at 5:40 PM Roman Shpount <> wrote:
>>> Part of the problem is that mmusic have decided to punt on the FQDN
>>> support. In the current mmusic-ice-sip-sdp the final language that was
>>> included:
>>> <connection-address>:  is taken from RFC 4566 [RFC4566].  It is the IP
>>> address of the candidate, allowing for IPv4 addresses, IPv6 addresses, and
>>> fully qualified domain names (FQDNs).  When parsing this field, an agent
>>> can differentiate an IPv4 address and an IPv6 address by presence of a
>>> colon in its value - the presence of a colon indicates IPv6.  *An agent
>>> generating local candidates MUST NOT use FQDN addresses.  An agent
>>> processing remote candidates MUST ignore candidate lines that include
>>> candidates with FQDN *or IP address versions that are not supported or
>>> recognized.  *The procedures for generation and handling of FQDN
>>> candidates, as well as, how agents indicate support for such procedures,
>>> need to be specified in an extension specification.*
>>> So, at this point we have two options:
>>> 1. draft-ietf-rtcweb-mdns-ice-candidates can update ice-sip-sdp and
>>> define how FQDN candidates generated by mdns are handled
>>> 2. write a new draft in mmusic which defines FQDN handling
>>> In any case some sort of mmusic discussion is needed to reconcile this.
>>> Best Regards,
>>> _____________
>>> Roman Shpount
>>> On Wed, Jul 3, 2019 at 8:28 PM Justin Uberti <> wrote:
>>>> The problem this draft is trying to solve is fairly RTCWEB-specific. If
>>>> there are individual issues to resolve, we can send them out to mmusic for
>>>> discussion, but AFAIK no changes to existing ICE specs are needed.
>>>> On Wed, Jul 3, 2019 at 4:26 PM Roman Shpount <> wrote:
>>>>> Hi All,
>>>>> Is rtcweb the right place for draft-ietf-rtcweb-mdns-ice-candidates?
>>>>> This entire draft seems to be ICE/SDP specific and not limited to rtcweb.
>>>>> Also, there are significant interop implications for this draft
>>>>> between browser and non-browser end points which probably warrant larger
>>>>> discussion outside of rtcweb group. I would think mmusic would be a much
>>>>> better place for this draft. I know there is an incentive to complete this
>>>>> draft quickly but this has a potential to break a lot of things (it already
>>>>> did break interop with almost every existing ICE implementation).
>>>>> Regards,
>>>>> _____________
>>>>> Roman Shpount
>>>>> _______________________________________________
>>>>> rtcweb mailing list