Re: WWAN, PPP, and IPv6 configuration questions

[Dan Williams <dcbw redhat com>]

On Thu, 2014-04-10 at 22:33 +0200, Bjørn Mork wrote:
> Dan Williams <dcbw redhat com> writes:
>
> > Hi Tore!
>
> I'm not Tore but I'm unable to shut up :-)
>
> > I'm slowly working on getting all the IPv6 pieces together and had a
> > question about PPP & IPv6 that you might know.  I'm using the
> > Icera-based Nokia 21M that you sent me long ago, and (due to some
> > ModemManager bugs) it's using plain PPP.
> >
> > 1) What should the prefix be for the IPV6CP assigned address?
>
> Huh?  IPV6CP doesn't assign or negotiate any address.  It negotiates an
> Interface Identifier.  Which can then be used to create an address along
> with a suitable prefix.  Like fe80::/64 for a link local address.  Or
> any global prefix received in an RA (although it's not mandatory to use
> it there)

Fair enough, that's what it does.  But we get to turn that into an
IPv6LL address that we can use for SLAAC, and that requires a prefix.

> > pppd
> > hardcodes it as '10' which seems entirely bogus to me:
> >
> >     memset(&ifr6, 0, sizeof(ifr6));
> >     IN6_LLADDR_FROM_EUI64(ifr6.ifr6_addr, our_eui64);
> >     ifr6.ifr6_ifindex = ifr.ifr_ifindex;
> >     ifr6.ifr6_prefixlen = 10;
> >
> >     if (ioctl(sock6_fd, SIOCSIFADDR, &ifr6) < 0) {
>
> Yup, this is a somewhat common misconception due to fe80::/10 being
> reserved for LL, as you noted.  But you absolutely do not want to accept
> an address in fe80::/10 which is outside fe80::/64 as valid.
>
> If you used /128 then the default route you got from the RA would stop
> working, wouldn't it?
>
> Use /64.

Yeah, that's what I ended up doing.  And it does appear to work.

Dan