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

[Syam Madanapalli <smadanapalli@gmail.com>]

Hi Tero,

> I'm starting to get so confused in the middle of this LinkID v.s.
> Landmark Prefix discussion that I'm afraid that I'm loosing my grasp
> even with the basics.
> 
> I started wondering what will actually happen in the following scenario:
> 
> 
> 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.

Either Landmark or Linkid approaches detect that there is no link
change. I think, as far DNA is concerned the job is done. 

> However, even though 'N' still in the same network, the address 'N' is
> using (prefix 2 based) is not valid anymore.

This is the host problem and is same problem if the router suddenly
stops advertising prefix 2. I looked into 2462bis and found the following 
text: 

5.5.3  Router Advertisement Processing

---

d) If the prefix advertised is not equal to the prefix of an address
      configured by stateless autoconfiguration already in the list of
      addresses associated with the interface (where "equal" means the
      two prefix lengths are the same and the first prefix-length bits
      of the prefixes are identical), and the Valid Lifetime is not 0,
      form an address (and add it to the list) by combining the
      advertised prefix with the link's interface identifier

If the node did not configure the address based on prefix 1 then
it should either wait till the prefix 2 life time expiry or if the router 
does not support forwarding for the prefix 2, an intelligent host can
configure new address using prefix 1 based on packet loss. I am
not sure about choosing new address based on packet loss.


> 
> As I said, I'm so confused that I can't even be sure if this has already
> been discussed on the list.
> 
> --
> Tero
> 
>