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Re: failure detection



On Tue, 30 Aug 2005, Erik Nordmark wrote:

The idea with *graceful* renumbering is that the admin knows in advance (hours, days, weeks) that the network will be renumbered and that there is some overlap when both prefixes work. The notions of preferred/deprecated/invalid prefixes in RFC 2462 was designed to handle this case.

In this model communication (including external) continues to work for the deprecated address up until that address becomes invalid.

The takeaway point is that forcing a deprecated address, by overloading with a notion of "failed", makes it impossible to tell graceful renumbering apart from something which a multihoming solution can repair.

Yes, agreed. A host wouldnt know the difference.

I'm wondering though, given the language in the RFC, why one would ever need to distinguish between a prefix no longer preferred due to failure and one no longer preferred due to renumbering? Eg, one way an administrator of a multihomed site (in lieue of shim6) might deal with a failure is to initiate graceful-renumbering ;).

The RFC provides a mechanism to indicate preference. Does it really matter for what reason a prefix no longer is preferred? It's a usage consistent with the mechanism, regardless of what that mechanism was specified for.

The intended use is outside of the mechanism, and not immediately important, surely? Nor is the reason for a renumbering that important either, surely?

Sorry to harp on about this, just a 'failed' bit has some problems - it requires that it wasn't the router<->host link which failed for one, and it seems to me that the high-level difference as to why a prefix should no longer be used is not that important.

regards,
--
Paul Jakma	paul@clubi.ie	paul@jakma.org	Key ID: 64A2FF6A
Fortune:
Truth never comes into the world but like a bastard, to the ignominy
of him that brought her birth.
		-- Milton