Subject: RE: ND- processing neighbor advertisements

From: Richard Draves <[email-masked]>
Date: Mon, 6 Dec 1999 10:14:42 -0800

> I agree with Rich; an implementation should change the state of an NCE
> from REACHABLE to STALE if
> 
> - we already have a REACHABLE NCE with a link-layer address,
> - we receive a neighbor advertisement for the neighbor but 
> with a different
>   address in the target link-layer address option, and
> - the override bit is zero.
> 
> regardless of the solicited flag of the NA.

I think we are not in agreement. You describe above the current MSR IPv6
behavior in this case. But the examples in my previous message show (I hope)
that it is desirable to do this when the solicited flag is clear, NOT
regardless of the solicited flag.

Rich
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From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Tue, 07 Dec 1999 11:16:36 +0900

>>>>> On Mon, 6 Dec 1999 10:14:42 -0800 , 
>>>>> Richard Draves <[email-masked]> said:

> regardless of the solicited flag.

I may have jumped to a conclusion when I read your (previous) mail,
but my understanding was as follows:

1. You said the appendix was wrong. The appendix specifies that we
   should change the state of an NCE *only* when receiving a
   solicited NA:

REACHABLE       NA, Solicited=1,        -                     STALE
                Override=0
                Different link-layer
                address than cached.

   but in fact the trigger by which we should change the state is
   reception of an *unsolicited* NA.

>>>>> On Thu, 2 Dec 1999 16:44:55 -0800 , 
>>>>> Richard Draves <[email-masked]> said:

> But I think the appendix has it backwards. In the above situation, you want
> to leave the NCE in the reachable state. It's when the solicited flag is
> zero that you want to change reachable -> stale.

2. (According to Rich's first mail) the current MSR implementation
   changes the state to STALE when receiving an unsolicited
   NA. (Actually it changes the state regardless of the solicited
   flag, but the behavior implies above.) So it is correct.

3. The only thing that you may want to change in the MSR
   implementation is about logging:

>>>>> On Thu, 2 Dec 1999 15:53:27 -0800 , 
>>>>> Richard Draves <[email-masked]> said:

> If the solicited flag is set in this situation, then we log a debugging
> event (it shouldn't happen in normal operation) but the value of the
> solicited flag doesn't change what happens to the NCE.

   As you said in a succeeding mail, you actually don't have to regard
   this as special, when you have more than one node that assigns an
   anycast address:

>>>>> On Thu, 2 Dec 1999 16:44:55 -0800 , 
>>>>> Richard Draves <[email-masked]> said:

> Well, I thought about this further and I think MSR IPv6 is doing the wrong
> thing in this situation. I said below that the solicited flag won't normally
> be set. Actually it can easily happen: when there are two instances of an
> anycast address on the link, and you send a NS for the anycast address,
> you'll receive two NAs. When you process the second NA, you'll be in exactly
> this situation - your NCE is REACHABLE (because you just processed the first
> NA), the override flag is clear, the solicited flag is set, and the target
> link-layer address is different than your cached link-layer address.

Or did you suggest that we *should not change* the NCE state from
REACHABLE to STALE when we receive a solicited (and Override=0,
different link-layer addr) NA?

					JINMEI, Tatuya
					Communication Platform Lab.
					Corporate R&D Center, Toshiba Corp.
					[email-masked]
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