Re: [DNA] draft-ietf-dna-cpl-02.txt

[Syam Madanapalli <smadanapalli@gmail.com>]

> > We present this as the most conservative approach and doesn't
> > recommend it. Even without the Complete Prefix List, it will take 4
> > secs to finish DNA according to our recommendation.
>
> So, it takes 4 seconds to complete  DNA? I thought the whole point was
> for DNA to complete quickly. Recall, using normal 2461/2462 in _MOST_
> cases, a single RS will trigger the transmission of RAs from _all_
> routers, and this will complete within .5 seconds. Thus, having DNA
> operate for 4 seconds seems to miss the bigger picture.

draft-ietf-dna-cpl-02 is for unmodified routers. Actual DNAv6 draft
can be found at

http://www.ctie.monash.edu.au/dna-dt/draft-pentland-dna-protocol3-pre02.txt

This protocol requires the modifications to both Routers (at least one
on the link)
and Hosts.

With this protocol, the host can make a link change decision with one
RS/RA exchange. This draft also defines Fast RA, which ensures that
two routers will not respond at exactly the same time while allowing
one of the routers on the link to respond immediately.


From the draft-ietf-dna-cpl-02
...
   MIN_DELAY_BETWEEN_RAS (3 Sec) + MAX_RA_DELAY_TIME (0.5 Sec)
   + network propagation delay is the maximum delay between an RS and
   the resulting RAs [1]. 4 seconds would be a safe number for the host
   to wait for the solicited RAs.  Assuming no packet loss, within 4
   seconds, the host would receive all the RAs and know all the
   prefixes.  Thus we pick 4 seconds as the value for MAX_RA_WAIT.
...

An implementation, may choose to compare the prefixes as and when
it receives an RA, if there is a common prefix, host can make the
decision that it is at the same link and need not wait for 4 sec.
4 sec wait may be required for the cases where there is a link change.

In most cases if the RA contains all the prefixes, the receipt of first
RA is sufficient to check for link change. In such cases a host can
wait for 4 sec to receive an RA, at that time the host can resend
the RS (the first RS might not have reached the router).

- Syam