Re: [DNA] RE: Review of draft-krishnan-dna-simple-01.txt

[JinHyeock Choi <jinchoe@gmail.com>]

Bernard

> [JC] However, from your remarks below, it seems that sometimes NS/ NA based
> decision overrules RA based decision.
>
> [BA] I think that an RA from a router will over-ride an NA from that same
> router, with respect to a given address.  But an RA from another router will
> not.

Then the host should treat RAs differently according to sending
routers. That entails added complexity, which, I'm not sure desirable.
Simple DNA is supposed to simplify DNA operation.

> [JC] ok. However this necessitates hosts to maintain the state of pairs, (a
> prefix, a router which advertise the prefix). Also if an RA with no
> known prefix arrives before a solicited NA, I assume the host
> immediately decides a link change, instead of waiting for the NA.
>
> [BA] The way I think of it is that the host needs to determine
> whether its existing addresses are valid.  It can determine that based
> on receipt of an NS from a router, or receipt of RAs.

From your remark, I assume that a host verifies its addresses one bye
one. The verification of one address doesn't guarantee the validity of
others, right?

This also entails added complexity. Previously DNA checks whether the
host still remains in the same link or not, then accordingly verify
(or invalidate) all its addresses at the same time.

> Let us assume that formerly router A announced a prefix from which the
> host formed address A.  Now with Simple DNA, the host tries to determine
> if that address is still valid.  In response to an RS, it receives an RA
> from that same router with no known prefix.  It can now conclude that
> address A is not valid, under the assumption that the prefix should have
> been included if the router was still advertising it.
>
> However, the host could also have formed another address B based on an
> announcement from router B.  With Simple DNA, the host sends a unicast NS
> to router B which responds with a solicited NA.  The host can now assume
> that
> address B is still valid -- unless it receives an RA from router B
> that is missing the prefix from which that address was derived.

IMO, the host can verify address B based on the verification of
address A. If address A and B were valid in the same link and address
A is proven still valid, it's reasonable to assume that address B also
is still valid (except in some corner cases.)

> [JC] Now I come to wonder why RA based decision is assumed definite. Maybe
> it's better to make NS/NA based decision takes precedents over RA
> based decision.
>
> [BA] Receipt of an RA is additional information which may invalidate an
> assumption made as a result of receipt of an NA.  For example, the RA
> could indicate different prefixes, or a change in address assignment
> mechanism (stateless to stateful or the other way around).

I have in mind the following example.

Assume a host is attached to a link
with two access router R1 and R2
which advertise prefix 1 and prefix 2 respectively.

The host autoconfigures address 1 with prefix 1.

After a while, the host executes DNA and performs NUD with R1 and R2.

When a solicited NA from R2 arrives to confirm R2's reachability,
IMO, it's reasonable to assume that
address 1 with prefix 1 is still valid,
even though a solicited NA from R1 didn't arrive yet (or never).

> In any case, I think it is important that we write all of this down in the
> Simple DNAv6 draft so that we can evaluate it and understand how well it
> works and under what conditions it might not work.

agree. I wish simple DNA operation is presented more clearly lest we
should argue over irrelevant issues.

Thanks for your kind consideration.

Best Regards

JinHyeock