Re: [2462bis] preferred lifetime and the 'two-hour' rule

> 1) update the preferred lifetime regardless of whether the valid
>    lifetime is accepted or not wrt the "two-hour" rule
> 2) update the preferred lifetime only when the valid lifetime is
>    accepted
> 3) leave this as implementation dependent

> The KAME/BSD implementation behaves as option 1.  However, it seems to
> me that option 2 makes much more sense because a rejected valid
> lifetime indicates a possibility of attack and the other parts of
> the information may then be bogus as well.  And, in fact, item 2 of

I'm trying to understand the utility/danger scale here.

An operational possibility is that somebody accidentally 
configures an incorrect prefix in a router and advertises that with the
default lifetimes (which are greater than 2 hours).
When that is detected a minute later the operator can
 - drop the valid lifetime on the hosts down to 2 hours (by starting to
   advertise the prefix with a 2 hour valid lifetime which decrements over
time)

If we take alt #1 then the preferred lifetime can be immediately dropped
to zero, which will stop the incorrect prefix from being used as a source
address for new communication (which is good).

Does alt #2 mean that the preferred lifetime would be 2 hours?
Or that the preferred lifetime could be announced as zero as long as the
valid lifetime is annouced with an acceptable value?
I think you are suggesting the second one.

And on the danger scale,
with alt. #2 an on-link attacker can cause immediate deprecation by
advertising the prefix with a valid lifetime = 3 hours and a preferred
lifetime = 0, so I don't think it makes a difference whether we choose
#1 or #2. 

I must be missing something.

  Erik

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