[gentoo-user] Re: To all IPv6-slackers among the Gentoo community

[Ian Zimmerman]

On 2019-11-28 04:11, Ralph Seichter wrote:

> > But what about connecting to the outside world? For that, the
> > link-local address doesn't work.
>
> It does work, actually. fe80::1 is a perfectly valid way to specify the
> default gateway. Remember that NICs have several IPv6 addresses with
> different scopes.

Sorry, I'm still confused :-(  My host has to set the source address
field in outgoing packets to something.  If it's the link local address
the router can't just forward it unmodified, or upstream routers and
hosts won't know where it originally came from.  What am I missing?

wikipedia:

  In a computer network, a link-local address is a network address that
  is valid only for communications within the network segment or the
  broadcast domain that the host is connected to.

As for fe80::1 being good as it is ...

 matica!8 lc$ route -6
Kernel IPv6 routing table
Destination                    Next Hop                   Flag Met Ref Use If
localhost/128                  [::]                       Un   0   2     0 lo
fe80::52e5:49ff:fec0:504d/128  [::]                       Un   0   3     0 enp2s0
fe80::/64                      [::]                       U    256 2     0 enp2s0
ff00::/8                       [::]                       U    256 2     0 enp2s0
[::]/0                         [::]                       !n   -1  1     0 lo
 matica!9 lc$ ping -6 fe80::1
PING fe80::1(fe80::1) 56 data bytes
From fe80::52e5:49ff:fec0:504d%enp2s0: icmp_seq=1 Destination unreachable: Address unreachable
From fe80::52e5:49ff:fec0:504d%enp2s0: icmp_seq=2 Destination unreachable: Address unreachable
From fe80::52e5:49ff:fec0:504d%enp2s0: icmp_seq=3 Destination unreachable: Address unreachable
From fe80::52e5:49ff:fec0:504d%enp2s0: icmp_seq=4 Destination unreachable: Address unreachable
From fe80::52e5:49ff:fec0:504d%enp2s0: icmp_seq=5 Destination unreachable: Address unreachable
From fe80::52e5:49ff:fec0:504d%enp2s0: icmp_seq=6 Destination unreachable: Address unreachable
^C
--- fe80::1 ping statistics ---
7 packets transmitted, 0 received, +6 errors, 100% packet loss, time 143ms
pipe 3
 matica!10 lc$ traceroute -6 fe80::1
traceroute to fe80::1 (fe80::1), 30 hops max, 80 byte packets
connect: Invalid argument

> > No configuration needed for this ULA thing? How does it happen, then -
> > is it implemented entirely in the kernel?
>
> Before I try to come up with my own explanation, I suggest you search
> for terms like Neighbor Discovery Protocol (NDP) and Stateless Address
> Autoconfiguration (SLAAC). The latter, for example, is the reason why
> DHCPv6 is often not necessary.

Ok, I'll do that ... I wonder if those can give me a real address though.

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