RE: [DNA] Prefix information for link identification in DNA

[Bernard Aboba <bernard_aboba@hotmail.com>]

>He thought that it is questionable to assume that:
>
>    1) Every network has a router.
>    2) you can name a network using one of its prefixes.

There are certainly adhoc networks in which there is no router.   However, 
detecting attachment to such a network is quite difficult, because nodes may 
join and leave and therefore there is no L3 invariant.  That is why the 
DNAv4 reachability test cannot be used to detect attachment to adhoc 
networks, but rather adhoc attachment is concluded after failiure of all 
other approaches (reachability test, DHCPv4, etc.)

I would also agree that there are situations in which a network cannot be 
named using one of its prefixes.  In DNAv4, a private network is not 
suitable for identification because it is not unique.

>So if a link has no router and no prefixes except the link-local
>prefix (which will be the same for all links) we have a problem.

I would say that a "problem" only occurs if DNA somehow makes the situation 
worse.  If a link has no router and no prefixes except link-local, then the 
best that can be achieved is for a host to utilize the link-local address.  
Unless DNA somehow impedes that, it may not do any good, but it also does no 
harm.

>I'm not sure what we can reasonably do at layer 3 if there is(are)
>no router(s) present on the link to help the hosts identify the
>link.  (Any ideas?)

The best you can do at L3 is to use a link-local address.