At Fri, 29 Jun 2007 12:06:21 -0400,
Ralph Droms <[EMAIL PROTECTED]> wrote:
> Stig - you wrote "At least as a sysadmin/user I would find it
> confusing if the prefix length I configured would not be used for on-
> link determination. I think it's more bad than good to try to
> separate the two. I'm happy the way it currently is on the systems
> I've seen." I can understand that it should be possible to manually
> configure on-link prefix information. I question whether that
> configuration should be conceptually tied with address assignment
> because of the design of IPv6, or do we mix address assignment with
> prefix information because that's the way it was done in IPv4?
I believe so. Even though the concepts of address/prefix are
different for IPv4 and for IPv6 in some points, I'm pretty sure that
an administrator would expect when they execute
# ifconfig ed0 inet6 2001:db8:1234::abcd prefixlen 64
the system treats 2001:db8:1234::/64 as on-link, just like they would
expect when they execute
# ifconfig ed0 inet 192.0.2.1 netmask 0xffffff00
the system treats 192.0.2.0/24 as on-link.
> Looking back to the definition of DHCPv6 - we received a lot of input
> that DHCPv6 should *not* include information about default routers
> and on-link prefixes, because that information comes from RAs. That
> argument made sense to me at the time; makes sense to me in the case
> of manual address assignment, too...
IMO the key difference is "automatic" (whether stateless or DHCPv6) vs
"manual". In the case of RA (for on-link prefix) + DHCPv6, everything
will be set up automatically, so I'd agree that it makes more sense
not to have the redundant information in DHCPv6. In the case of
manual configuration of addresses, the administrator should be able to
control everything, so I think it's reasonable for the administrator
to allow to specify both the address and on-link prefix information
even when the node is also receiving RAs.
BTW: I personally think this situation (manual address assignment with
RA for on-link info) is very atypical and is not really appropriate to
compare with the common case for DHCPv6(address) + RA(on-link) in the
first place. But if the administrator really wants to do it, they can
achieve the result by specifying 128 as the prefix length:
# ifconfig ed0 inet6 2001:db8:1234::abcd prefixlen 128
at least on BSDs.
Finally, I'd like to note that prefix information option with L=0 does
not mean the correspondent prefix is off-link.
[...] Note, however, that a Prefix Information option
with the on-link flag set to zero conveys no information concerning
on-link determination and MUST NOT be interpreted to mean that
addresses covered by the prefix are off-link. The only way to cancel
(Section 6.3.4 of RFC2461)
So, by executing
# ifconfig ed0 inet6 2001:db8:1234::abcd prefixlen 64
(while receiving RAs with the prefix information for 2001:db8:1234::/0
and L=0)
the administrator is not "overriding" the information advertised by
the RA; they are simply "specifying" the information which has not
been provided.
JINMEI, Tatuya
Communication Platform Lab.
Corporate R&D Center, Toshiba Corp.
[EMAIL PROTECTED]
--------------------------------------------------------------------
IETF IPv6 working group mailing list
ipv6@ietf.org
Administrative Requests: https://www1.ietf.org/mailman/listinfo/ipv6
--------------------------------------------------------------------
