Re: [MMUSIC] FQDN support in ice-sip-sdp

[Roman Shpount <[e-mail]>]

On Thu, Apr 11, 2019 at 4:05 AM Christer Holmberg <
[e-mail]> wrote:

> > Add a candidate extension which specifies candidate address type,
> something like addrtype which can be set to
> > "inipv4" or "inipv6". If IP address is used and it does not match the
> addrtype candidate extension, this candidate is
> > ignored. When FQDN is used, it is resolved using A DNS request when
> addrtype is inipv4 or not present and using
> > AAAA DNS request when addrtype is inipv6. Address family in c= line,
> when FQDN is a default candidate must be
> > IN IPV4 if addrtype is inipv4 or not present, and must be IP IPV6 if
> addrtype is inipv6
> >
> > Example:
> > a=candidate:2319437384 1 udp 2122260223
> 8a2fd7b5-41d5-4c15-ad83-d33a0d66a75a.local 60454 typ host inipv4
> > a=candidate:2319437384 1 udp 2122260223
> 8a2fd7b5-41d5-4c15-ad83-d33a0d66a78b.local 60454 typ host inipv6
> >
> > This keeps each candidate line to one address and works in cases when
> FQDN resolves to one IPv4 and one IPv6 address
> > due to something like DNS64.
>
> So, if I understand you correctly, you are suggesting that the one
> providing the FQDN candidate splits it into two separate candidates (two
> a=candidate lines when SDP is used), and the remote peer will process them
> as two separate candidates, but if DNS returns both an IPv4 and IPv6
> address the peer will only use the IP version indicated by the address type
> ("inipv4" or "inipv6").
>

I am suggesting that:

If agent is dual stack, it can include the same FQDN in two candidate lines
with different address types, effectively creating two candidates. If agent
is single stack or if FQDN is supposed to resolve to an address of specific
address family (different FQDN for IPv4 and IPv6), agent will create a
single candidate line with this FQDN and address family.

On the receiving side, if candidate includes addrtype inipv4, an A DNS
request is sent to resolve FQDN. If more then one result is returned, this
candidate is ignored. If single result is returned, it is an IPv4
candidate. If candidate includes addrtype inipv6, an AAAA DNS request is
sent to resolve FQDN.  If more then one result is returned, this candidate
is ignored. If single result is returned, it is an IPv6 candidate.

Corrected Example for a dual stack agent (note different foundation,
priority and port for two candidates with the same FQDN ):

 a=candidate:2 1 udp 2129033471 alice.comany.biz 60460 typ host addrype
inipv4
 a=candidate:1 1 udp 2129289471 alice.comany. biz 60454 typ host
addrype inipv6

Regards,
_____________
Roman Shpount