[Cerowrt-devel] IPv6 address assignment and naming

Dave Taht dave.taht at gmail.com
Fri Aug 16 15:13:49 EDT 2013

Dear Juergen:

Your note kind of opens a can of worms.

On Fri, Aug 16, 2013 at 11:13 AM, Juergen Botz <jurgen at botz.org> wrote:

> On 08/16/2013 03:06 PM, Dave Taht wrote:
> > You need to statically assign addresses on the AHCP server box.
> Ok, fair enough... but then why did it work without statically
> assigned addresses in 3.7.x?
> :j
The desired state of integration with the openwrt developers was not
achieved? :/

Since January there has been a huge amount of work into making a better
state machine for openwrt, called netifd, to make it more possible to have
many more complex behaviors when it came to dealing with network


I'm very happy with how well that's working out, but it was a scary switch
at the time!!

But this obsoleted the ahcpd integration I'd had before, and the "ahcpd"
proto has not made it into the mix of supported protocols in netifd. A
script that interfaces with the netifd concepts doesn't exist. AHCPd itself
could use a bit of work in this area, too. It would be nice in particular
if dyamic ipv6 assignment could be made to work, that would lead to a
natural syntax stanza in /etc/networks of something like:

config interface 'gw01'
        option proto 'ahcp'
        option ip6assign '128'

config interface 'gw11'
        option proto 'static'
        option ip6assign '128'

My thought originally was to just fold ahcpd into dnsmasq, but I spent a
grand total of a day on it and realized that it was harder than I thought.
Second thought was to make ahcpd listen on the netifd message bus, that too
was harder than I thought. Neither is "hard", actually, but it needs some
focused time by someone, preferably not me. Juliusz went to ietf hoping to
convince someone that dhcpv6 and SLAAC are not the answer to all things
(which I agree with), but there was insufficient time to present on the

AHCPD is a zillion times easier to use than dhcpv6, particularly in meshy
environments, it's also more effective.

While most of the ipv6 stuff in openwrt is going increasingly well, AND we
just got working multi-prefix routing fixed in the linux kernel (not sure
if the IPV6_subtrees spatches are committed or backported yet), there are
still integration hassles with ipv6 going on. (I expect integration hassles
for years, actually - dealing with the pure dynamic assignments the isps
are demanding is nearly impossible)

In particular the ongoing work on dnsmasq is now out of sync with the
6relayd work and vice versa. Back in january, when we obsoleted radvd, it
looked like dnsmasq was going to take over ipv6 ra, dhcpv6, and naming
duties, but 6relayd then made serious progress and does most of that itself
and is (at least presently) more tightly integrated with openwrt than
dnsmasq is.

On the one side, I strongly support tight naming integration with ipv6
address assignment, which is why I like the dnsmasq integration (which is
what cerowrt uses). Naming is a real pita with ipv6. (The ipv6 folk have
spent a lot of time NOT thinking about it.). I would like ahcpd to also
support some level of naming, too.

On the other, I like several things that 6relayd does that dnsmasq can't
(and probably shouldn't)

On the gripping hand, the elephant in the room is decent multicast dns and
service discovery over ipv6, and mdnsext over routed networks in general.
http://tools.ietf.org/html/draft-cheshire-mdnsext-hybrid-02 - avaha is
huge, and buggy, and the mac guys have mdns figured out pretty good, so it
would be best (IMHO) to follow their lead....

I really don't know what to do about all that!

I tried to get the core developers of these tools to drink some beer and
bang their heads together at that ietf, don't know if that happened. cc-ing
a couple here. Cerowrt exists to test this sort of stuff. At the moment,
though, figuring out how to backport the ADSL htb fixes from Linux 3.11
into 3.10 is on my mind higher... and doing one more teeny fix to codel, as

Seeing ipv6_subtrees work was very exciting, it's going to make things like
mptcp and vpns and multiple exit gateways work much better on ipv6, enable
a whole new generation of usefulness in ipv6 routing protocols, etc -



The overall "fight" vs a vs ahcpd is that the path homenet is on is to drag
in an entire routing protocol (ospf) just to do ipv6 prefix assignment, and
methods for carrying other useful configuration information around have not
been well defined.

So this was juliusz's argument, unpresented:


I have always thought ahcpd was a good start, but far from complete, and
dhcpv6 hopelessly overengineered and worse, inappropriate for the wireless
age. I also have no idea what to do about that!

Welcome to future. You can help shape it, if you choose.

/me pulls a pillow over his head

Dave Täht

Fixing bufferbloat with cerowrt:
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