Subject: issue 43 - certs vs. RA prefix checks

From: <[email-masked]>
Date: Fri, 19 Dec 2003 17:57:16 +0200

Jonathan Trostle wrote:

> there's no mention (from my quick read of the
> spec.) regarding whether the host checks that the router advertisement
> (and other NDP message) prefixes are contained in the router
> certificate prefixes or ranges. If not, what action does the host
> take?  Suggestion: if not, the host MUST find a new router.

I agree. I modified the draft as follows to reflect
this:

http://www.arkko.com/publications/send/issues/issue43diff.html

This change relates to the reception of a PI within an RA. Question:
what other situations require this check? Redirect?

--Jari

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From: "James Kempf" <[email-masked]>
Date: Fri, 19 Dec 2003 08:49:45 -0800

Yes, Redirect requires it as well.

            jak

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From: Jari Arkko <[email-masked]>
Date: Fri, 19 Dec 2003 20:18:02 +0200

> Yes, Redirect requires it as well.

Hmm... does this always apply? What if R1 (who has a cert
only for P1) sends a redirect regarding P2, and there's some
other router R2 thas has a cert for P2.

--Jari

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From: "James Kempf" <[email-masked]>
Date: Fri, 19 Dec 2003 10:28:31 -0800

Wouldn't H need to have a cert for R2 that listed the prefixes before
executing the Redirect?

I suppose one could argue that since R1 is trusted, H should trust it's
recommendation of R2, but this gets into the issue of transitivity, which is
a little tricky. 2461 actually does not require H to send a Router
Solicitation to R2, so the base spec has the issue of trust transitivity in
it.

            jak

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From: Jari Arkko <[email-masked]>
Date: Sat, 20 Dec 2003 00:18:13 +0200

> Solicitation to R2, so the base spec has the issue of trust transitivity in

Lets think about this again. What is a redirect, really? Its not a
declaration of the advertised prefixes of a router. Its a declaration that
you should a given destination is behind another router. So in this
case the Redirect Destination Address may have nothing to do with the
prefixes assigned to the router. Clearly, we are not certifying routing
tables in SEND... Also, the Target Address field is the link-local
address of the better router, so this address can not be compared to
the certificate ranges either.

So one could perhaps make the conclusion that Redirects do not
need to be checked for consistency to the cert address ranges.

However, there is one complication: the usage of Redirect to
announce that the destination is really on-link. In this case
Target Address equals Destination Address. It seems weird that
a certified router (prefix = P) could not advertise a prefix Q
(P != Q) but could send a Redirects to everyone who wishes to
send packets to Q. And tell them that Q is really on link.

So this leads me to believe that some new text is needed for
the Redirect case. See for yourselves:

Am I missing something, or is this everything?

--Jari

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From: "James Kempf" <[email-masked]>
Date: Fri, 19 Dec 2003 14:34:15 -0800

Jari,

This looks OK. Rereading 2461 more carefully, I now see that, as you state,
the Redirect only applies to a particular destination address, and not for
changing the default router. So, I agree that there isn't a need for prefix
checking, except when informing the node that a particular prefix is on
link.

The proposed text looks fine.

            jak