Re: Confirmation to advance: draft-ietf-6man-ipv6only-flag-05

[David Farmer <[e-mail]>]

On Wed, May 8, 2019 at 5:30 PM Brian E Carpenter <
[e-mail]> wrote:

> David,
>
> > A host that receives any RAs with the flag set to 1
>
> No! That must be
>
> A host that receives only RAs with the flag set to 1
>
> It is an absolute requirement that all routers must agree that the flag is
> 1, or else it has no effect.
>
> Otherwise I'm sympathetic to your rewrite, but I see little point in
> updating the draft until the WG Chair gives us a read-out on the rough
> consensus.
>

Because with this flag now only being a secondary signal and the lack of
any DHCPOFFERS is now the primary signal, it is safe to allow any RA set to
1 to trigger no longer auto-configuring an IPv4 Link-Local address, this
only has an effect if the host also doesn't receive any DHCPOFFERS. So, if
the host receives one RA with the flag set and one RA with the flag
cleared, the host should continue sending DHCPDISCOVERS perodically and
configure an IPv4 address if it gets any DHCPOFFER. However, if it never
gets any DHCPOFFERS it should not auto-configure of an IPv4 Link-Local
address, even though there are conflicting settings of this flag in the RAs.

This at least partially mitigates the malicious sending of an RA with the
flag cleared on an IPv6-Only network, again the lack of DHCPOFFERS controls
if the host configures an IPv4 address or not, this flag only says what to
do if you don't receive any DHCPOFFERS and whether or not to continue
sending periodic DHCPDISCOVERS. Further, you should only stop sending
DHCPDISCOVERS if the flags in RAs received all agree.

Thanks.

-- 
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