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

Roman Shpount <> Fri, 01 February 2019 04:43 UTC

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From: Roman Shpount <>
Date: Thu, 31 Jan 2019 23:43:13 -0500
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To: Justin Uberti <>
Cc: "Dale R. Worley" <>, RTCWeb IETF <>, mmusic WG <>
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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 Thu, Jan 31, 2019 at 10:58 PM Justin Uberti <> wrote:

> We can however all agree that "c=IN IP6" is busted:
I guess one way to interpret this that each address should have a MDNS
alias. So, if you are dealing with dual stack host, it should provide two
MDNS candidates, one of which is IPv4 and another IPv6. The c= line should
specify FQDN for one of those candidates and specify the type (IP4 or IP6).

There are two problems:

1. There is no way to know which address type is in the candidate-address
when FQDN is used there. Guidance in ice-sip-sdp is talking about the
presence of column in IP6 address, but this definitely does not apply to
FQDN. It would've been better to specify something like local4 and local6
as FQDN suffix in MDNS alias to specify the candidate-address type so that
correct DNS request can be issued.

2. A lot (if not most) SDP/ICE implementations do no support parsing FQDN
in candidate-address or c= line. This might create interop problems since
RFC 5245 specified that candidate-address is an IP Address.

Roman Shpount