[arch-projects] [netctl] Regarding commit fe5f0d6fe - "Restrict dhcpcd to IPv4"

Thomas Bächler thomas at archlinux.org
Sun Jun 16 05:20:02 EDT 2013

Am 16.06.2013 11:00, schrieb Jouke Witteveen:
> On Sun, Jun 16, 2013 at 10:55 AM, Thomas Bächler <thomas at archlinux.org> wrote:
>> Am 16.06.2013 10:35, schrieb Jouke Witteveen:
>>>> What this doesn't mention is that it also reads DNS servers from Router
>>>> Advertisements, which the kernel cannot do by itself. dhcpcd does not
>>>> perform dhcpv6 as far as I know.
>>> I'm not sure; it might do so nowadays. Does dhclient read DNS servers
>>> from RAs in IPv4 mode?
>> I haven't check what dhclient does, but dhcpcd is definitely not a
>> dhcpv6 client.
> http://roy.marples.name/projects/dhcpcd/wiki/DhcpcdFeatures
> It says it is

That's interesting, I haven't seen the manpage refer to this at all. It
lists the RFCs for everything it supports: DHCP, BOOTP, Router
Solicitation - no mentions of dhcpv6.

And then, there's the source code: dhcpcd-5.6.8/ipv6rs.c, line 819ff:

        if (rap->flags & (ND_RA_FLAG_MANAGED | ND_RA_FLAG_OTHER)) {
                if (new_data)
                            "%s: no support for DHCPv6 management",

So, if your router advertises that dhcpv6 is available ("managed" or
"other" flag), dhcpcd simply prints "no support for DHCPv6 management"
to your syslog.

If we keep our current approach, removing the -4 from dhcpcd in
IP6=stateless mode (or even in all cases with IP6 != no) will only be

> In that case, it would be nice if dhcpcd allowed more control over
> what it does do and what it doesn't. In IPv4-only configurations, I
> don't want dhcpcd to assign an IPv6 address.

I think we should rethink our approach. In a non-static setup, why do we
even want to configure ipv4 and ipv6 separately, when our dhcp clients
can do it all combined? Sure, some people want to disable ipv4 or ipv6,
but we can still allow that.

Even explicitly configuring whether you want stateful or stateless
configuration in IP6= doesn't serve much purpose: Once you get a Router
Advertisement, it tells you whether stateful configuration is possible
or even necessary. The user does not need to supply this information, as
his network topology already knows - of course, you'd need a client that
understands this information, which doesn't seem to be available *shrugs*.

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