Re: Bug#632915: ifupdown: DHCPv6 support
Please remember to CC the bug report on replies. I wouldn't object to
being CCed as well.
On Thu, Jul 07, 2011 at 10:39:44AM +0200, Bjørn Mork wrote:
> Bjørn Mork <bjorn@mork.no> writes:
> > Colin Watson <cjwatson@ubuntu.com> writes:
> >> I was initially going to support wide-dhcpv6-client as well as
> >> isc-dhcp-client, but it was rather harder to integrate into ifupdown,
> >> since doing stateful DHCPv6 there requires writing out custom
> >> configuration files rather than just passing the right command line
> >> options. isc-dhcp-client is Priority: important, so this ought to be
> >> good enough for most people.
> >
> > Nope, sorry. isc-dhcp-client has no support for ppp interfaces, which
> > makes it useless for lots of people. See e.g. xs4all's IPv6 access
> > service.
OK. Thanks for that feedback. (That said, I don't think this needs to
block deployment of DHCPv6 support in ifupdown; wide-dhcpv6-client
support seems to fall in the category of things that can be added later
without compatibility problems, and adding isc-dhcp-client support does
not make things any worse for wide-dhcpv6-client users.) Do you know if
anyone is working on PPP support in isc-dhcp-client? I can't find a bug
report for it.
It is, incidentally, unfortunate that dhcp6c does not wait for a lease
before daemonising. dhclient's behaviour is distinctly superior here
from the point of view of integrating it into the boot process. With
dhcp6c, you have the choice between running it in the foreground and
having to mess about with process supervision, and running it as a
daemon and carrying on with other work before the interface is actually
up. Neither is very appealing.
> And to provide a solution instead: Yes, wide-dhcpv6-client will require
> a config file. But the version packaged in Debian does not need require
> a *custom written* one. It has support for "profiles", and you can get
> away with a static config like this (note: no interface specific info
> here):
>
> profile default
> {
> send ia-na 0;
> };
>
>
> and a command line like this:
>
> dhcp6c -P default $IFACE
It appears that it would still need to be custom-written, as at the
moment the dhcp6c.conf shipped in the Debian package does not contain
such a profile. I would rather avoid ifupdown having to write out a
profile fragment.
In the stateless code, I also have to trust that nobody has modified the
'default' profile to be stateful, otherwise things will go wrong.
Do you think it would be appropriate to append this to the stock
dhcp6c.conf? The duplicate 'profile stateless' is to avoid ambiguity in
case somebody has modified 'profile default'.
profile stateless
{
information-only;
request domain-name-servers;
request domain-name;
script "/etc/wide-dhcpv6/dhcp6c-script";
};
profile stateful
{
send ia-na 0;
request domain-name-servers;
request domain-name;
script "/etc/wide-dhcpv6/dhcp6c-script";
}
id-assoc na 0 {
};
There are other packaging issues that need to be addressed before we
could add wide-dhcpv6-client support to ifupdown (CCing the maintainer).
wide-dhcpv6-client installs into /usr, making it unsuitable for
infrastructural use on a system with a separate /usr. That will
presumably need to be changed. Unfortunately, ifupdown's execable()
function takes an absolute path, so there would be a compatibility
problem if we added support to ifupdown first. We should probably fix
execable() to do a full $PATH search for non-absolute paths.
It is not clear to me how to handle multiple interfaces.
wide-dhcpv6-client ships an /etc/wide-dhcpv6/dhcp6c-ifupdown script
which uses dhcp6ctl to talk to a running dhcp6c client. I see no way to
run two clients at once and still use dhcp6ctl: dhcp6c doesn't document
a way to change the port it listens on, and in any case having to
configure this from ifupdown would be tedious. wide-dhcpv6-client ships
an init script, and may already be configured to run as a daemon on many
systems. You can only pass the profile to dhcp6c, not dhcp6ctl, so if
you need to run stateless DHCPv6 on one interface and stateful DHCPv6 on
another then it looks like you need to run multiple dhcp6c processes at
once. Is this supported? If so, what is the supported way to stop one
of multiple existing dhcp6c processes, bearing in mind that 'dhcp6ctl
stop' won't work for the reason just given? We'll need to do that on
ifdown.
In general, I think somebody who knows WIDE well needs to figure out how
it could be nicely integrated into ifupdown.
/etc/wide-dhcpv6/dhcp6c-ifupdown is a reasonable stopgap, but it doesn't
seem to fit well with configuring stateless/stateful DHCPv6 in
/etc/network/interfaces the way I propose, which is the neatest fit I
can think of to the /etc/network/interfaces model.
Thanks,
--
Colin Watson [cjwatson@ubuntu.com]
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