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List:       ietf
Subject:    Re: Tsvart last call review of draft-ietf-ice-rfc5245bis-16
From:       Ben Campbell <ben () nostrum ! com>
Date:       2018-01-30 16:49:40
Message-ID: 8154BE03-5B04-4AE0-B936-804820ED907F () nostrum ! com
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Commenting on the first issue:

> On Jan 30, 2018, at 8:34 AM, Christer Holmberg <christer.holmberg@ericsson.com> \
> wrote: 
> > Significant Issues:
> > 
> > A. Section 5.2:
> > 
> > Lite implementations only utilize host candidates.  A lite
> > implementation MUST, for each component of each data stream, allocate
> > zero or one IPv4 candidates.  It MAY allocate zero or more IPv6
> > candidates, but no more than one per each IPv6 address utilized by
> > the host.  Since there can be no more than one IPv4 candidate per
> > component of each data stream, if an ICE agent has multiple IPv4
> > addresses, it MUST choose one for allocating the candidate.  If a
> > host is dual-stack, it is RECOMMENDED that it allocate one IPv4
> > candidate and one global IPv6 address.  With the lite implementation,
> > ICE cannot be used to dynamically choose amongst candidates.
> > Therefore, including more than one candidate from a particular scope
> > is NOT RECOMMENDED, since only a connectivity check can truly
> > determine whether to use one address or the other.
> > 
> > I find it quite strange that the above text says there can only be single
> > IPv4
> > based candidate, while for IPv6 a LITE implementation may have one
> > candidate
> > per IPv6 address. Isn't the LITE implication of having multiple
> > candidates for
> > the same address family similar? Yes, IPv6 kind of forces the need for
> > dealing
> > with multiple IPv6 addresses on any host. However, I can see that certain
> > servers will actually be multi-homed in IPv4 and thus can in a sensible
> > way
> > actually have multiple IPv4 candidates, and let the clients select which
> > interface has the best reachability.
> > 
> > Can you please be explicit on what in ICE prevents things to work for
> > IPv4 but
> > the same case works for IPv6?
> 
> This is text from RFC 5245. I agree it is confusing, and unfortunately I
> don ¡ ¯t have a good answer.
> 
> I guess my approach would be to suggest that we simply remove the
> restriction. In addition, there is generic text about dual-stack etc
> elsewhere,
> and I don ¡ ¯t see anything ICE lite specific.
> 
> OLD:
> 
> "Lite implementations only utilize host candidates.  A lite
> implementation MUST, for each component of each data stream, allocate
> zero or one IPv4 candidates.  It MAY allocate zero or more IPv6
> candidates, but no more than one per each IPv6 address utilized by
> the host.  Since there can be no more than one IPv4 candidate per
> component of each data stream, if an ICE agent has multiple IPv4
> addresses, it MUST choose one for allocating the candidate.  If a
> host is dual-stack, it is RECOMMENDED that it allocate one IPv4
> candidate and one global IPv6 address.  With the lite implementation,
> ICE cannot be used to dynamically choose amongst candidates.
> Therefore, including more than one candidate from a particular scope
> is NOT RECOMMENDED, since only a connectivity check can truly
> determine whether to use one address or the other."
> 
> 
> NEW:
> 
> "Lite implementations only utilize host candidates.
> With the lite implementation, ICE cannot be used to dynamically choose
> amongst candidates. Therefore, including more than one candidate from a
> particular IP address family is NOT RECOMMENDED, since only a connectivity
> check can Truly determine whether to use one address or the other."
> 

We should avoid making non-critical changes to text that was unchanged from 5245 at \
this point in the process. If people think this is important to change, it needs \
working group discussion. This is a hazard of bis drafts—it's really hard to tell \
when you are done. :-)

I am guessing that the original motivation was that, since ICE-lite cannot select \
among candidates, you want the minimum number of candidates necessary per address \
family. Multiple IPv6 candidates are allowed because of the nature of IPv6. But I \
think if you are truly multi-homed, you probably shouldn't be using ICE-lite.

Ben.


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