ipv6/ppp: FreeBSD obtains linklocal on tun0 only

O. Hartmann o.hartmann at walstatt.org
Sun Dec 2 21:37:20 UTC 2018

Hash: SHA512

Am Fri, 30 Nov 2018 16:41:02 +0000
"Bjoern A. Zeeb" <bzeeb-lists at lists.zabbadoz.net> schrieb:

Sorry for the late reply, had a long weekend off ...

> On 30 Nov 2018, at 15:59, Christoph Moench-Tegeder wrote:
> > ## O. Hartmann (ohartmann at walstatt.org):
> >  
> >> As far as I know, with the IPv4 stack a IPv4 address is obtained
> >> automatically, so I would expect the same for IPv6.  
> >
> > The fun with "automatically" is that there's more than one way...
> > DHCPv6 and NDP (IPV6 Neighbour Discovery Protocol/Router Solicitation)
> > have been mentioned, the third option is IPV6CP (PPP options, just as
> > PPP-with-IPv4 does with IPCP). I've no idea what your provider does, so...  
> No, IPV6CP, to my very best 15 year old memory only negotiates the
> interface identifiers, which are used to generate the link-local addresses.
> There is no negotiation for full prefix/global addresses, hence it is
> different to the IPCP NCP used for IPv4.

In my case. IPV6CP indeed does only negotiate the linklocal addresses (fe80::) on my
WAN interface ...
> One wants to run rtsol on the link and then depending on the O/M bits possibly
> also DHCPv6 I’d assume.
> There’s a couple of other options and shortcuts, on how to configure global
> addresses (as always, if you know you have a static prefix assigned, one can
> do it by hand for example);  and then there are shortcuts as to when you’d
> perform DAD, which shouldn’t bother the user.  These days there should also
> be options with regards to RFC4941 (privacy extensions for stateless address
> autoconf).

Studying the manpage for ppp(8), one might not get that IPV6CP does only negotiate the
IPv6 linklocal address ...

> It may no be uncommon to run the ptp-link with link-local addresses only and
> configure an address from a prefix on lo0 or the internal interface only; but
> I am doubtful FreeBSD’s userland implementation is that sophisticated.
> /bz
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- -- 
O. Hartmann

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