Subject: RE: RFC 2461- issue list: Prefixes with L=0

From: Soliman Hesham <[email-masked]>
Date: Mon, 3 Nov 2003 09:11:51 -0500

> Something about prefixes with L=0 are confusing to me. Kindly see
 > below.  
 > 
 > 1. The prefixes with L bit off. 
 > - The meaning/ purpose of prefixes with L=0 is not exactly clear 
 >    to me. What's the use of non-on-link prefixes for a node? 
 > 
 > 2. The prefixes assigned to more than one links.
 > - According to RFC 2461, it's legitimate to assign a prefix 
 > (with L=0) 
 >    to two separate links. But it's not clear to me on what condition 
 >    can we do this.   

=> Actually, I think the L flag is a really powerful feature.
Basically when it indicates that a prefix is not on-link
it is informing hosts that they should send their traffic
to the default router. This is useful for the case you mentioned
where a prefix is assigned to more than one link (e.g. multi-link
subnets/ND proxying devices). 

 > 
 >  I wish we clarify the above. The prefixes with L=0 makes DNA work 
 > complicated. Though they are troublesome, I am afriad that, 
 > in wireless
 > environment, we can't avoid them.

=> If it is found that in some deployment cases the L=0 
causes problems, the network admin is free to configure
the routers accordingly and always use on-link prefixes.
This is completely under the control of the admin. 
I think Fred Templin sent a question some time ago
on this and Thomas explained how hosts should handle the
case where the L flag is set to zero. We can add this clarification
in the new revision if that helps.

If there are other scenarios where this is problematic
please send them to the list.

Thanks,
Hesham

 > Best regards
 > JinHyeock

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From: "JinHyeock Choi" <[email-masked]>
Date: Mon, 3 Nov 2003 23:42:36 +0900

Dear Hesiam

Thanks for your prompt reply. 

> to the default router. This is useful for the case you mentioned

If the purpose of prefixes with L=0 is to inform hosts to send traffic 
to the default router, why not omit those prefixes altogether from 
RAs. Host will send the packets destined to unknown prefixes to a 
default router anyway.  
 
> This is completely under the control of the admin. 

I wonder that there may be some wireless links on which admin can't 
assign on-link prefixes. For example, a link with hidden node problem 
like 802.11 b ad-hoc mode or bluetooth.  

> in the new revision if that helps.
 
Fred Templin raised the issue whether it's possible to advertise a prefix 
with L=0 and A=1 and Thomas said so. Is this what you have in mind? 
And I think the prefix with L=0 and A=1 may cause unnoticed address 
duplication. 

Best regards

JinHyeock

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From: Fred Templin <[email-masked]>
Date: Mon, 03 Nov 2003 11:54:30 -0800

>in the new revision if that helps.

Thomas' explaination did indeed clear my confusion on this subject.
A clarification in the new revision would seem to put the issue to
rest, IMHO.

Fred
[email-masked]