Re: [DNA] DNA proposal issue 19 - was [Issue X] LinkID v.s. LandmarkPrefix

[Erik Nordmark <erik.nordmark@sun.com>]

JinHyeock Choi wrote:

> No, Linkid has a rule to prevent "Renumbering and Early reassignment." 

I agree that Linkid (as well as CPL I think) has a recommendation to the 
administrator to not reassign a prefix to another link in less than 3 hours.
I'm not sure the same text is in the landmark draft yet, but it would be 
trivial to add.

But my concern is what happens should the administrator not follow this 
recommendation.

The worst case would be when P1 and P2 are assigned to link1, and P2 is 
immediately reassigned to link3 (which had prefix P3 before), at about 
the same time that the a host moves from link1 to link3.

In that case, any prefix based scheme for link identification (CPL, 
landmark, linkid, or anything else we can invent) can get into trouble, 
by the host assuming that P1, P2, and P3 are assigned to link3.

Should this happen, then the host will assume that P1 is usable until 
the last valid/preferred lifetimes it saw has expired. Since RFC 2461 
suggests a default preferred lifetime of 7 days, the host will try to 
use P1 as a source address for 7 days, even though no packets returned 
to P1 will make it back to the link to which the host is attached.

We could decide this is the administrators fault, and not do anything. 
Or we could add a mechanism to attempt to detect this and recover in 
less than 7 days.

But the problem certainly isn't specific to any particular proposal, 
since they all rely on prefixes for link identification. And I suspect 
that we have the same choices in terms of solutions independent of which 
proposal we apply this to.

    Erik