ip6mode in rc

[Mihai Chelaru]

Hi,

I'm missing the purpose for the ip6mode mode in our rc scripts. Why
shouldn't one be allowed to use rtadvd and rtsol for different
interfaces, for example ? If it's about tweaking inet6 sysctl tree it
should be done with rc.d/sysctl script. Am I missing something
elementary here or is it OK to drop support for this automagic ?

[Greg Troxel]

Post by Mihai Chelaru
shouldn't one be allowed to use rtadvd and rtsol for different
interfaces, for example ? If it's about tweaking inet6 sysctl tree it
should be done with rc.d/sysctl script. Am I missing something
elementary here or is it OK to drop support for this automagic ?

As I understand it the v6 specifications define the notion of router vs
host as a serious distinction, and ip6mode sets a number of defaults.
ip6mode=router forces v6 forwarding on. autohost sets up the machine to
take router advertisements, and there is a complaint if one has rtsold
w/o autohost.

Is there something that you want to do that is difficult to do now? I
have been running a number of v6 routers and hosts and not been having
problems.

The only thing I can think of is trying to set up a router where one
interface uses stateless autoconfiguration. This is a bizarre setup
that the specs as I remember say one shouldn't do.


I think it's good that someone can just set ip6mode=autohost in rc.conf
and then have functioning v6, without having to muck with sysctls.

[Mihai Chelaru]

Post by Greg Troxel
As I understand it the v6 specifications define the notion of router vs
host as a serious distinction, and ip6mode sets a number of defaults.
ip6mode=router forces v6 forwarding on. autohost sets up the machine to
take router advertisements, and there is a complaint if one has rtsold
w/o autohost.

The serious distinction refers mostly to the router advertisments case
if I remember correctly.

Post by Greg Troxel
Is there something that you want to do that is difficult to do now? I
have been running a number of v6 routers and hosts and not been having
problems.

No, when I needed both rtsol and rtadvd, I modified the rc scripts and
got rid of ip6mode.

Post by Greg Troxel
The only thing I can think of is trying to set up a router where one
interface uses stateless autoconfiguration. This is a bizarre setup
that the specs as I remember say one shouldn't do.

That's exactly the example I'm referring to. Yes, I know that dhcpdv6 is
prefered over rtsol in this case (and probably in all cases) but that's
another discussion.
Moreover, one can be surprised to find out that he can't forward packets
and also have an interface autoconfigured (the router + rtsol case),
especially if that interface is not taking active part in routing
process.

Post by Greg Troxel
I think it's good that someone can just set ip6mode=autohost in rc.conf
and then have functioning v6, without having to muck with sysctls.

You also have to add rtsol=YES and probably change rtsol_flags if you
don't want to autoconfigure all interfaces. So, all sysctls can be done
separately in a rtsol script - and there's just one sysctl to muck with
in this case. So, it looks to me like one more line to write in this
case.

For router case, I don't understand why one has to do different for ipv4
and ipv6. If you muck with sysctls for v4, do the same for v6. Why
should one set a variable in rc.conf in order for network script to set
a sysctl flag ? I strongly believe that we should minimize difference
between v4 and v6 procedures - including startup configs and different
utilities like ping-ping6, traceroute-traceroute6.

Don't think that I have a teeth against it. If you or someone else find
these options useful, it's fine for me, I just want to understand the
logic behind their long and happy existence.

[Hubert Feyrer]

Post by Mihai Chelaru
I'm missing the purpose for the ip6mode mode in our rc scripts. Why
shouldn't one be allowed to use rtadvd and rtsol for different
interfaces, for example ? If it's about tweaking inet6 sysctl tree it
should be done with rc.d/sysctl script. Am I missing something
elementary here or is it OK to drop support for this automagic ?

What's wrong with it?


- Hubert

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[der Mouse]

Post by Mihai Chelaru
That's exactly the example I'm referring to. Yes, I know that dhcpdv6
is prefered over rtsol in this case (and probably in all cases) but
that's another discussion.

Well...preferred by some people.

Post by Mihai Chelaru
For router case, I don't understand why one has to do different for
ipv4 and ipv6.

In a practical sense, you don't, mostly.

However, (my impression is that) there are some voices in the v6
community who think pushing their religion of how a network ought to be
set up is more important than people having functional networking
working the way they want; these are the people who, for example, will
tell you that every broadcast domain needs its own /64, even though
that is not actually true (my house LAN, for example, is using a /96).

Unfortunately some of these voices are in positions of (relative)
power, so some aspects of their religion end up being imposed on
everyone, even those for whom it's a bad fit.

Some things do have to be different because v4 and v6 _are_ different,
but, for the most part, you can pretend that v6 is just v4 with funny
addresses and get by (though you will fail to get some of the nice
things v6 offers over v4, of course). Most of the differences fall
under the "as if" rule because they're not visible outside your border.

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