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Date: Tue, 8 Apr 2014 11:38:41 -0400
From: Rich Felker <>
Subject: Re: if_nameindex/getifaddrs and dhcpcd issue

On Tue, Apr 08, 2014 at 03:16:10PM +0100, Justin Cormack wrote:
> On Tue, Apr 8, 2014 at 2:42 PM, Rich Felker <> wrote:
> >> and it only needs to read ipv4 addresses,
> >> unless it is implementing dhcp6 too, maybe it does now. Again dhcp6
> >> needs netlink, the Musl ipv6 parts for getifaddrs already use /proc
> >> which is definitely unreliable for early boot config in a distro in my
> >> view.
> >
> > In what way does dhcp6 need netlink? What's made this discussion
> > difficult so far on IRC is assertions of that form (although not the
> > same one) without an explanation of why it's believed to be true, so
> > I'd like to keep rational discussion possible by making sure that such
> > claims are backed up by explanation rather than just stated as fact.
> I was under the impression that the ioctl-based interface for ipv6 is
> incomplete under Linux.

Probably "incomplete" in a sense that it can't do some special-purpose
stuff that most users don't need. Busybox entirely avoids netlink, as
far as I can tell, and it's perfectly acceptable for setting up ipv6,
at least in simple setups. You don't even need busybox's iproute2
workalikes; ifconfig and route work fine.

> That does not mean anything needs to be in
> libc though. ISC dhcp for v6 just calls out to ip in scripts, rather
> than ifconfig that it uses for v4, so it is indirectly uses netlink,
> but does not require any libc support, indeed all the C code is
> portable.

udhcpcd works the same; it doesn't make any changes to the interfaces;
it just speaks the dhcp protocol. This is really the correct


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