4 Jul
2019
4 Jul
'19
5:53 p.m.
Sorry long long post. tl;dr 2 default IPv6 routes different metrics set up
persistent on Debian.
I need a bit of advice concerning routing IPv6.
Here is the problem. I do quite a bit of travelling around and a lot of it
in SE Asia. I frequently find my self where the relevant ISP does not
provide IPv6 connectivity. Even here at home my connection will
occasionally change my address or I have to reboot the router and get a
different one. I do things over the net for which I want IPv6, but also for
DNS I need a stable fixed address.
So I have an additional /56 subnet allocated to my VPS. Over the years I
have tinkered with different VPN solutions to push these addresses down to
my home network. I have found a different solution which not only was easy
to set up, but works a dream except for one tiny issue.
The /56 has been added to eth0 of my VPS. I am running wireguard and have
it set up interface wg0 to which I route a /60 subnet. <bitfolk
prefix>:e10::/60. Packets hitting this are encrypted with the server key
and then encapsulated in IPv4 UDP packets and sent to the wg0 interface on
my home machine, decrypted and if meeting criteria move through firewall
etc. Sending out it is the same in reverse, encryption being via the client
keypair. The client wg0 has subnet <bitfolk prefix>:e10::2/64, the server
only accepting packets from this range and properly encrypted.
Now here comes the problem. It is the default route issue. All that I read
says that you cannot have 2 default routes in the same table. I have looked
at a variety of solutions but find none except the one everyone seems to
say is impossible but which works. I set the route
*ip -6 route add ::0/0 dev wg0 metric 512. *
Note the metric 512. The autoconfigured one has a metric of 1024. which
gives me
*ip -6 routedefault dev wg0 metric 512 pref mediumdefault via
fe80::42c7:29ff:fe26:78c9 dev enp3s0 proto ra metric 1024 expires 265sec
mtu 1488 hoplimit 64 pref medium*
When I have finished fiddling and checking I will change the wg0 route to
metric 2000 so that traffic will normally go through the main interface and
when that has no IPv6 connectivity or is playing up, the wg0 route will be
selected, (I hope).
My 2 laptops, and Raspberry Pi will then be set up with their own wg1 etc
interfaces and will then have their own /64 subnets.
But when I try to get the route established automatically through the
wireguard conf files or through PostUp I get the message can't do it as
there is already an autoconfigured default. So I am stuck, at the moment
with adding manually after every boot/reboot. Any suggestions please?
VPS running Debian Stretch This box at home running Debian Buster.
The only answer I can think of at the mo is turn off autoconfig, but then I
lose this fallback mechanism and add difficulties with communicating with
mobile phone/router etc. Or I guess I could forget the fancy fall back idea
and just go through VPS but that could add a long delay when doing ordinary
surfing. IPv4 of course just goes out through the normal interface