Subject: RE: Making ND Optional [Was RE: draft-ietf-ipv6-cellular-host-00. txt -> wg last call?]

From: Margaret Wasserman <[email-masked]>
Date: Tue, 05 Mar 2002 10:24:06 -0500

Hi John,

>    This router 
>    most likely will not be a final destination for the host's traffic. 
>    Additionally, due to special characteristics of the cellular link, 
>    lower layer connectivity information should make it unnecessary to 
>    track the reachability of the router. 

We have defined a mechanism to locate and maintain reachability 
information about neighbours in IPv6, called "Neighbor Discovery".  
This isn't an optional part of IPv6 that it would be appropriate 
to disable on a particular link type.

However, it is expected for ND to receive "advice" from other layers
regarding the "reachability" of another host -- so it would be
great if the L2 mechanism gave ongoing advice to IPv6 regarding
the reachability of the router, which would result in suppressing
IPv6 NS messages.

I don't believe that your conclusion is sound...

>Therefore, Neighbor 
>    Solicitation and Advertisement messages MAY be implemented for the 
>    cellular interface. 

An implementor could read this and believe that it was acceptable
to build a 3GPP cell phone (with only one cellular interface) that
didn't even contain the _code_ necessary to generate IPv6 NS and
NA messages.

What happens when that host receives an NS message?

Do you think that people may ever want to set-up redundant
3GPP networks, or make a choice between two possible 3GPP
routers, based on their current reachability?  If you don't
use ND, how will this information be available for IPv6
routing decisions?

There seems to be a mis-perception in the 3GPP community that
ND will result in a lot of extra traffic.  The idea of ND is
to locate the other node _once_ and maintain reachability 
information about that node on an ongoing basis, using advice
from other layers, _without_ sending additional ND messages
unless absolutely necessary.

Are there reasons why you think that this won't work on 3GPP
hosts?

>In addition, a cellular host SHOULD NOT send the 
>    link layer sub-option on its cellular interface, and SHOULD silently 
>    ignore it if received on the same interface.

This is fine, and would be an excellent piece of information
to put in a standards-track "IP over <foo>" document.
    
>2.6 RFC2462 - IPv6 Stateless Address Autoconfiguration 
>     
>    IPv6 Stateless Address Autoconfiguration [RFC-2462] MAY be 
>    supported. 

This should be a MUST.  IPv6 hosts MUST support address autoconfiguration,
although it is possible for the routers to be configured so that it isn't
used (if desired).

>    A cellular host SHOULD NOT perform Duplicate Address Detection on 
>    its cellular interface, as each delegated prefix is unique within 
>    its scope when allocated using the 3GPP IPv6 Stateless Address 
>    Autoconfiguration. 

Will the router end of the link allocate any addresses within the
unique /64 assigned to the PDP context?  If so, what mechanism will
be used to ensure that the host doesn't allocate the same address?

If it's actually true that a conflict can never occur, then we should
indicate that DAD won't be used on these link types in an 
"IPv6 over <foo>" document, as previously discussed.

Margaret

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From: "Charles E. Perkins" <[email-masked]>
Date: Tue, 05 Mar 2002 10:42:26 -0800

Hello,

Disclaimer: I am not fully caught up on this discussion.

I hope that cellular hosts would be able to run DAD and ND
whenever they need to.  I would hope that the IETF would
not approve a document that says "some" IPv6 hosts MUST NOT
(or even SHOULD NOT!) implement DAD/ND.  This would be a
problem, if for instance some operators would then use it
to DISALLOW IPv6 addressable devices from running those
protocols.  They could claim non-conformance to RFC nnnn!
I reckon that it would be better to determine certain
conditions under which an IPv6 node would experience
better performance by not running those protocols, but
still to expect the protocols to be part of the IPv6 node
implementation.

My own interest lies in having the ability for some 3G
device to serve as a router for personal devices that
I may carry with me.  I'd also like for those devices
to be autoconfigurable, and to find the 3G router by
using standard techniques.  All of this could be done
so that my devices would share the same prefix as my 3G
router device.  Why not?

Again, please excuse if this is all duplication of previous
discussion.

Regards,
Charlie P.