Subject: RE: Issue 13: Omission of prefix options - resolution

From: Soliman Hesham <[email-masked]>
Date: Fri, 7 Nov 2003 03:50:05 -0500

> Host nodes should not be doing this?  We did not put this in 
 > ND for very
 > good reason. We want to reduce what Hosts no about prefixes 
 > and leave to
 > the stateless and stateful. Why do we want to put this into 
 > HOsts.  What
 > is the reason.  That is not below.

=> I should have described the scenario a bit better. 
This is a case where hosts need to know whether they have
changed links or not. The only way we know that today is 
through the contents of the RA. Hosts today use the prefixes 
advertised (or not) as an input to the movement detection algorithm
amongst other things. There are different flavours of movement
detection depending on how conservative an implementor wants 
to be. But in all those flavours, the prefix option (or absence
of) may well trigger the algorithm. 

I don't have a strong opinion on whether this should go into
2461bis or not. But I do think that there is a problem. Another
consideration is how _real_ this problem is. Does anyone know of 
a router implementation that sometimes does not advertise 
all options to save BW ? 

 > What problem is this addition trying to fix or solve?  
 > 
 > I have read the draft below and believe the core issue is resolved.
 > What prefixes are supplied is in the system not the host or 
 > why not just
 > use DHCPv6?  

=> DHCPv6 can be used, but in order to trigger DHCPv6 a host
needs to know that it has changed links. Otherwise it will
be triggered unnecessarily. 

   I think we cannot and must not overrule the essential
 > meaning of the A and M bits.

=> Agreed. We won't do that.

 > 
 > In fact I suggest in additon to each member of this list a problem
 > statement be stated for each change to 2461.

=> I'll try to cover that briefly in a "background" section
when I send a suggestion to resolve an issue.

Hesham 

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From: Markku Savela <[email-masked]>
Date: Fri, 7 Nov 2003 11:29:26 +0200

> From: Soliman Hesham <[email-masked]>

> Does anyone know of a router implementation that sometimes does not
> advertise all options to save BW ?

The problem is not with single router. It's with multiple routers and
this change requiring them to be in synch and advertising complete set
of each others prefixes.

And as I mentioned earlier, if I attach some dead end lan segment to
an existing link using the preferred route option, I don't want this
router to be inconvenienced by forcing it also to advertise all
prefixes. It would just send this preferred route option without any
prefixes.

As compromise, I could accept that a router, which knows it is
advertising all valid prefixes on the link, could set some "complete
bit" in RA. However, it must always be legal send incomplete RA's,
too.

In my view:

MIP6 detecting a movement by sniffing RA, and not finding the current
CoA among the prefixes, is wrong approach. If layer2 singals are not
available, I would think some type of link-id option is better
approach. You could have totally independent MIP6 beacon sender, that
would only send RA's without prefixes, containing only the Link-ID (to
make this beacon very short). Or, preferrably, the beacon should be
sending some totally new MIP6 specific ICMP6 message type.

Those links that wish to support movement, would install the beacon
sender, independently on any routers on the link. Of course, the Home
Agent would be obvious beacon sender.