Re: [DNA] [Issue X] LinkID v.s. Landmark Prefix

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

Tero Kauppinen (JO/LMF) wrote:

> Let there be two routers, 'A' and 'B' and some access points. 'A'
> advertises prefixes 1 and 2 whereas 'B' advertises prefix 3. After
> connecting to an AP host, 'N', sends an RS and gets an RA (from 'A'),
> and finally configures an address (basing on prefix 2). In the case of
> LinkID 'N' gets the current link-id prefix from the RA, and in the case
> of Landmark Prefix 'N' chooses a landmark prefix. Let's assume that
> prefix 1 is both the smallest prefix and the prefix 'N' chooses to be
> the landmark prefix. 
> 
> If we then say that 'A' stops advertising prefix 2 and zero-lifetime
> messages disappear, what will be the outcome? I mean, 'N' could attach
> to another AP, send an RA and learn that it's still in the same network.
> However, even though 'N' still in the same network, the address 'N' is
> using (prefix 2 based) is not valid anymore.
> 
> As I said, I'm so confused that I can't even be sure if this has already
> been discussed on the list.

My tongue in cheek answer is that this is a feature of RFC 2461 :-)
Even if there was no DNA, or there was DNA and the host didn't move to a 
different AP, the host would continue to use prefix2 until it expired.
This could be viewed as a feature in RFC 2461 in that even if a router 
fails and stops advertising a prefix for some time, it will not upset 
the configuration of the hosts unnecessarily. So when the administrator 
wants to remove a prefix, she has to explicitly configure the routers to 
drop the lifetime to zero (either abruptly or gradually).

The narrow path I've tried to follow is to realize the above issue, but 
yet make sure that DNA doesn't get any more confused by this then a host 
would get that doesn't move. For instance, by looking at how a 
non-moving host would behave when it attaches to the network.

But I might be making the wrong call here, and that in the light of 
intermittently connected hosts and lossy (radio) links, we should make 
the reverification of being connected to the same "place" a lot less 
forgiving.

    Erik