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Re: Next steps on the IPv6 Node requirements draft

    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).


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