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Re: Next steps on the IPv6 Node requirements draft



I agree with kre - address configuration through DHCP (confrolled
by 'M' bit) and autoconfiguration through advertised prefixes
should be considered independent.  An interface may well have
both autoconfiguration addresses and addresses obtained through
DHCP (and manually configured addresses, as well).

BTW, is there a differentiation here between the behavior of
hosts and routers in the processing of advertised prefixes and
the 'M' bit?  Is that differentiation explicitly documented
somewhere?  Is the node requirements document sufficiently
clear?

- Ralph

At 05:56 PM 6/19/2003 +0700, Robert Elz wrote:
>     Date:        Wed, 18 Jun 2003 17:23:05 -0700
>     From:        Alain Durand <Alain.Durand@Sun.COM>
>     Message-ID:  <3EF10269.8050106@sun.com>
>
>   | So what if the M bit is set _and_ a prefix is advertized?
>   | Should the node give up its stateless autoconfigured address in favor of
>   | DHCP?
>
>No, it should do both.
>
>   | What about statically configured addresses on the same node?
>
>It should keep that as well, though often if there's to be static
>config it will often also be the case that use of stateless autoconfig
>and dhcp config will be disabled (either explicitly or implicitly)
>
>   | IMHO, it makes little sense to have both a DHCP allocated address and a
>   | stateless autoconfigured address on the same interface.
>
>In that case, you wouldn't config your routers to send the M bit, and
>prefixes with the A bit set, at the same time.
>
>On the other hand, others may consider it useful to allow nodes to
>autoconfigure themselves addresses (so they always gave one, provided
>there's a working router to make the address useful) and at the same
>time, provide specific addresses to specific nodes (attempting to use
>DHCP doesn't necessarily mean the DHCP server will actually allocate
>an address) where specific nodes are expected to own well known addresses.
>
>   | However, I see cases where you want
>   | to have nodes using DHCP and nodes using stateless autoconfiguration on
>   | the same link.
>
>The very nature of *stateless* autoconfig is that there's no (easy) way to
>configure a node to not do it (manual config on that node excepted).   If
>there was, it would not be stateless.   So, by default, if any node on a
>link is permitted stateless autoconfig (of a prefix) all nodes are.
>
>It is generally harmless to own an extra address though, having the
>statelessly configured one, as well as a dhcp supplied one should not
>cause any harm.
>
>That is, I don't think receiving a DHCP allocated address should cause
>an autoconfig'd address to be dropped, there's no need (doing do raises
>all the questions of what you do if you've been running using the
>autoconfig'd address for hours when the dhcp server returns to life
>and allocates you an address).
>
>All that being said - a request to implementors out there.   It would be
>very (*very*) nice to have the ability in a node to ignore prefixes
>that are being advertised from routers, and never autoconfig an address
>in that prefix.   That is, I occasionally see someone advertising a
>prefix that I know doesn't work (they're getting ready for the day it
>will work, and have just jumped the gun - believing in early preparation
>or something).   I'd like to be able to ignore that (no matter what
>router advertises it - so lower level packet filtering doesn't help).
>
>kre
>
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