Re: Disabling ip4 and IPV6 on F20RC1

[Tore Anderson <tore fud no>]

* Pavel Simerda

> I don't have an IPv6-enabled PPP connection right at hand but I think
> I've seen a working setup without one. But I'm not going to set up
> one right now, so there's no point in arguing over that. I guess the
> simple fact that you technically don't need link-local addresses for
> global routing doesn't help you.

Here's a real-world example of why link-local addresses may be needed:

In 3GPP mobile networks, the network will assign an Interface ID to the
node. I'm no 3GPP expert like Bjørn, but I believe this information is
is carried in PCO, which is then bridged into e.g. IPV6CP if we're
talking PPP. The node is *required* to construct a link-local address on
its mobile interface using this network-assigned Interface ID. So if the
network has assigned an Interface ID of ::a:b:c:d, the mobile node
*must* configure the link-local address fe80::a:b:c:d if it is to comply
with the specs.

Now, my own mobile provider (or probably more correctly, the GGSN vendor
used by my mobile provider) does assume that mobile nodes adhere to the
spec. Because of this, it will unicast the RAs it emits to the
link-local address it expects the mobile node to have configured (i.e.
fe80::a:b:c:d in this case). Now, if the mobile node has played fast and
loose with the standards and skipped configuring this link-local
address, its IP stack will discard the inbound ICMPv6 RA packets as "not
addressed to me". Therefore, it will never see the Prefix Information
Option in the RA, which is the *only* way global addresses is signaled
to the nodes in 3GPP mobile networks. So the node will end up without
any IPv6 address at all (neither global nor link-local), and thus
without any usable connectivity.

I am not disputing that you've seen a working PPP connection without
link-locals. There are probably many situations where IPv6 will work
just hunky-dory without any link-local addresses configured. But that's
besides the point I'm trying to make; just because it works in one place
doesn't mean it will work in another. So a piece of software like NM,
which will be used all over the place, ought to adhere to the specs as
closely as possible, in order to get maximum compatibility with the
various networks it might end up being used in.

Tore