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Re: Gateway disappears on IPv6



On Sat, Jul 15, 2017 at 07:31:29PM +0200, Rainer Dorsch wrote:

> > I added a IPv6 support to a KVM virtualized Jessie system following the
> > instructions by the hoster
> > 
> > https://www.netcup-wiki.de/wiki/Zus
> > %c3%a4tzliche_IP_Adresse_konfigurieren#IPv6%7C

That should still work, but I see it uses the ancient interface alias
notation (like eth0:1). The example given there can be rewritten to a
more modern form:

allow-hotplug eth0
iface eth0 inet static
	address 37.100.195.4/22
	gateway 37.100.192.1

iface eth0 inet static
	address 46.38.240.15

iface eth0 inet6 static
	address 2a03:4000:2:11c5::1/64
	gateway fe80::1

Note that the netmasks and broadcast addresses are gone, and you can
have multiple inet stanzas for the same interface.

> > root@netcup:~# /sbin/route -6
> > Kernel IPv6 routing table
> > Destination                    Next Hop                   Flag  Met  Ref Use If
[...]
> > ::/0                           fe80::1                    UGDAe 1024 3   0   eth0

The flags field contains the letter 'e', which means that this route
expires. This is added by the kernel, most likely because the gateway
address is not inside 2a03:4000:2:11c5::/64, and will cause it to remove
the route after a while. This looks like the same issue reported in
Debian bug #378506, which is fixed in stretch.

The workaround is to remove the gateway fe80::1 statement, but to add
this instead:

	up ip -6 route add default via fe80::1 dev $IFACE onlink

-- 
Met vriendelijke groet / with kind regards,
      Guus Sliepen <guus@debian.org>

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