Subject: Question about precluding use of autonomous address-configuration

From: Ralph Droms <[email-masked]>
Date: Mon, 31 Oct 2005 14:17:17 -0500

Suppose the nodes on a link are to be restricted to the use of addresses
assigned through DHCP, and precluded from the use of autonomous address-
configuration.

It seems there are two ways to accomplish this goal:

1) Don't include any prefixes in router advertisements

2) Include the prefixes assigned to the link in router advertisements,
   with the A (autonomous address-configuration) flag set to FALSE

There may be a subtle problem with (2): the text in RFC 2462 does not
include RFC 2119 words absolutely precluding the use of autonomous
address-configuration:

    a) If the Autonomous flag is not set, silently ignore the
       Prefix Information
       option.

Note the lack of "MUST" before "silently ignore".

Is there a reason to prefer one of these two ways of precluding the use
of autonomous address-configuration?  Is there a problem with using
technique (1)?

- Ralph

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From: Doug Barton <[email-masked]>
Date: Mon, 31 Oct 2005 13:11:03 -0800

> assigned through DHCP, and precluded from the use of autonomous address-

I can also think of a third case, addresses are assigned statically.

> of autonomous address-configuration? 

I think that having a clean way of distinguishing "this is information only"
from "use this prefix" in RA is a good thing, so I'd prefer option 2. I can
think of several ways in which knowing the prefix would be useful to a host
that is not doing autoconf. One off the cuff example would be configuring a
host to append some static bits to whatever prefix is announced by the router.

hth,

Doug

-- 

	If you're never wrong, you're not trying hard enough