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

[Sander Steffann <[e-mail]>]

Hi Mark,

> Blocking 0x800/0x806 on individual link-layer ports would prevent IPv4
> traffic including link-layer broadcasts on the link, but it doesn't
> stop hosts initialising their IPv4 stack and trying to acquire an IPv4
> address via DHCP. It requires link-layer per-host port configuration,
> which would involve configuring 100s if not 1000s of individual ports.

Most switch operating systems and/or automation solutions provide easy ways to do that, but let's look a bit further.

> RFC2563 should stop an IPv4 host sending IPv4 packets after the
> initial DHCP transaction. However, it doesn't prevent link-layer
> broadcast DHCPDISCOVERS, which is flooded to all other hosts on the
> link and has to be processed by their main OS CPU to be discarded,
> because the NIC can't filter them using the DA. This is where the main
> battery cost will be when mobile nodes join the link, likely
> continuously on big Wifi networks at e.g. conferences.

Do you have numbers on this? I'd like to see whether this is a significant drain on batteries.

> A link with a DHCPv4 server on it supporting RFC2563 is not an IPv6
> Only link, because IPv4 is still present on the link. There should be
> no IPv4 services/infrastructure and no IPv4 packets on an IPv6 Only
> link, including IPv4 zero-conf link-local traffic. An IPv4 only
> zero-conf printer should not work on an IPv6 Only link, intentionally.

This is what I consider an overly restrictive view ("purist") of an IPv6-only link. Telling your clients that ask for IPv4 using DHCP that there isn't any isn't an operational problem.

> The combination of those two mechanisms would go close to achieving what this flag would, except that the first mechanism prevents the
> second from working.
> 
> So individually or in combination, neither of these are a solution to
> the problem of achieving an IPv6 only link.

Ok. SAVI then instead of full ethertype filtering. Widely implemented and it allows DHCP, DHCP filtering and if the clients don't get addresses assigned it will drop their traffic.

Cheers,
Sander

PS: it's almost 3am here. Don't expect more replies until tomorrow :)