Subject: [MMUSIC] ICE passive and multihoming

From: Eric Rescorla <[email-masked]>
Date: Mon, 27 Nov 2006 08:39:49 -0800

ICE-12 currently implies that you can't be multihomed and do passive-only
ICE:

   o  A passive-only agent obtains candidates just from its host
      interfaces, just like it would do without ICE.  It doesn't need to
      implement the STUN Binding Discovery usage [11] or the relay usage
      [12] to gather server reflexive or relayed candidates.  It needs
      to assign its candidates a foundation ID; however it can use the
      IP address itself as the foundation ID.

   o  The prioritization in Section 5.2 is trivially accomplished for
      passive-only agents utilizing RTP.  The type preference is set to
      126 and the local preference to 65535, resulting in a priority of
      2130706431 for RTP and 2130706430 for RTCP.

   o  In use candidates Section 5.3 are trivially selected - they are
      equal to the host candidates.

This logic wouldn't work if you had more than one IP. 

I understand from talking to JDR that this is an intentional choice
to require multihomed endpoints to do full ICE. It's not clear to
me that that follows directly from the idea of having a reduced 
ICE version for fully-connected elements. 

Does the WG have opinions on this?

-Ekr

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From: Jonathan Rosenberg <[email-masked]>
Date: Mon, 27 Nov 2006 17:10:17 -0500

Its worth clarifying a few things here.

Firstly, if the agent has both v4 and v6, it still doesn't need ICE. It 
can use ANAT, RFC 4091, and list a single candidate for each m-line (one 
for v4, one for v6).

If, for a particular IP version, the agent is multihomed, it requires 
full-mode if it wants to actually offer a candidate on each of its 
interfaces, and let ICE figure out which to use. My view was, for 
gateways and similar boxes today that are multihomed, they choose a 
specific interface on which to allocate a port, and use that. There is 
no need to dynamically discover which one to use. Consequently, with 
ice-passive, they'd continue to pick one and list a single candidate for it.

Thus, I do not think this restriction limits the applicability of 
passive-only mode.

Thanks,
Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                   600 Lanidex Plaza
Cisco Fellow                                   Parsippany, NJ 07054-2711
Cisco Systems
[email-masked]                              FAX:   (973) 952-5050
http://www.jdrosen.net                         PHONE: (973) 952-5000
http://www.cisco.com

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From: Eric Rescorla <[email-masked]>
Date: Mon, 27 Nov 2006 14:14:58 -0800

Jonathan Rosenberg <[email-masked]> writes:

> Firstly, if the agent has both v4 and v6, it still doesn't need
> ICE. It can use ANAT, RFC 4091, and list a single candidate for each
> m-line (one for v4, one for v6).
>
> interfaces, and let ICE figure out which to use.

Hmm.... I must be missing something because it's not clear to
me why that's true.

-Ekr

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From: Jonathan Rosenberg <[email-masked]>
Date: Mon, 27 Nov 2006 17:54:34 -0500

> Hmm.... I must be missing something because it's not clear to

I messed up here. Let me restate.

If, for a particular IP version, the agent is multihomed, if requires 
full mode ONLY IF it wants to offer, for a particular media stream, 
multiple candidates, one from each of its interfaces. If the agent is 
multihomed, but only wants to offer a single candidate for a particular 
media stream (thus choosing one of its interfaces), it can stick with 
passive-only.

-Jonathan R.

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From: Philip Matthews <[email-masked]>
Date: Wed, 29 Nov 2006 16:24:28 -0500

I am happy with these restrictions for passive mode.
If an endpoint wants to offer multiple candidates per stream,
and wants ICE to select one of them,
then I think it is reasonable to require it to implement full ICE.

- Philip

On 27-Nov-06, at 17:54 , Jonathan Rosenberg wrote:

> If, for a particular IP version, the agent is multihomed, if  
> requires full mode ONLY IF it wants to offer, for a particular  
> media stream, multiple candidates, one from each of its interfaces.  
> If the agent is multihomed, but only wants to offer a single  
> candidate for a particular media stream (thus choosing one of its  
> interfaces), it can stick with passive-only.
>
> -Jonathan R.
>
> --