Subject: RE: Comments on draft-ietf-6man-subnet-model-07

From: "Wes Beebee (wbeebee)" <[email-masked]>
Date: Mon, 4 Jan 2010 08:42:24 -0600

The problem is - without something like this, it's impossible to ever
expire a prefix or make sure that something is, indeed, off-link.

- Wes 

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Christian Huitema
Sent: Thursday, December 24, 2009 4:15 PM
To: Hemant Singh (shemant); Thomas Narten
Cc: Erik Nordmark; IPv6 Maintenance WG
Subject: Comments on draft-ietf-6man-subnet-model-07

This draft addresses a clear failure mode: a host believes that a
destination is on-link when in fact it is not, resulting in failure to
communicate. That's good. However, I have some doubts about one of the
recommendations:

   2.  In the absence of other sources of on-link information, including
       Redirects, if the RA advertises a prefix with the on-link(L) bit
       set and later the Valid Lifetime expires, the host MUST then
       consider addresses of the prefix to be off-link, as specified by
       the PIO paragraph of section 6.3.4 of [RFC4861].

Strictly implemented, this means that if a local router fails, then
hosts on the same link will stop communicating, when in fact they
should. In other words, this rules introduce fate sharing between local
connections and the local router. I don't think this fate sharing is
desirable.

-- Christian Huitema

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From: "Hemant Singh (shemant)" <[email-masked]>
Date: Mon, 4 Jan 2010 09:21:52 -0600

Thomas, 

We have to add an item to the Errata in RFC 4861 because Appendix F from
RFC 4861 that you quoted below refers to RFC 4942 when it should be RFC
4943.  One more thought from me.  If one has a router in one's network,
then such a routed network typically has the sys admin plan for the
router failure.  A routed network will re route to another router on
failure of one router and thus for your problem described below the new
router will take over.  If a router failure is not planned by the sys
admin of the network, then what Thomas and Wes are saying is applicable.

Hemant