Subject: preferred lifetime > valid lifetime

From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Tue, 10 Dec 2002 21:38:26 +0900

Hello,

I have a question about a corner case of IPv6 Neighbor Discovery; what
should a host do if a received RA contains a prefix whose preferred
lifetime is larger than valid lifetime?

In terms stateless address autoconfiguration, the specification
clearly says that such a prefix must be ignored:

    c) If the preferred lifetime is greater than the valid lifetime,
       silently ignore the Prefix Information option. A node MAY wish to
       log a system management error in this case.
(RFC 2462 Section 5.5.3)

However, there seems to be no description about the case in RFC 2461.
This is perhaps intentional, because the preferred lifetime does not
affect on-link prefix configuration.  So my question is:

- is RFC 2461 intentionally silent about the case of preferred
  lifetime > valid lifetime?
- if so, what should a host do when, for example, it receives a prefix
  with the L bit being set, the A bit being set, and preferred LT >
  valid LT?  Should it just regard the prefix as on-link and not
  configure a corresponding address?
- or, do I miss something in RFC 2461?

Thanks,

					JINMEI, Tatuya
					Communication Platform Lab.
					Corporate R&D Center, Toshiba Corp.
					[email-masked]

p.s. our implementation currently ignores such a prefix in terms of
prefix configuration (RFC 2461) as well.
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