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I wanted to assign Unique Local Addresses (ULA) to a couple of machines inside my LAN alongside the link-local ones and the globally routable ones. I am currently running dual stack.
I also wanted to keep them short, like fd69:6666::.

One machine is running Debian Jessie (kernel 3.16.0-4-amd64) and the other one Linux Mint 17.2 (kernel 3.16.0-38-generic x86_64).

After following this guide:
https://www.jumpingbean.co.za/blogs/mark/set-up-ipv6-lan-with-linux
i ended up with the following configuration:

/etc/network/interfaces:

allow-hotplug eth0
iface eth0 inet static
address 192.168.1.100
netmask 255.255.255.0
broadcast 192.168.1.255
gateway 192.168.1.1
dns-nameservers 192.168.1.1

auto eth0
iface eth0 inet6 static
address fd69:6666:: #fd69:7777:: on the other machine.
netmask 64

/etc/radvd.conf:

interface eth0
{
    AdvSendAdvert on;
    prefix fd69:6666::/64 { #fd69:7777:: on the other machine.
        AdvOnLink on;
        AdvAutonomous on;
    };
}

Problem is that i end up having both machines with the fd69:6666 prefix and nothing else! IPv6 connectivity stops working.
What am i doing wrong?

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Try using fd69::6666 instead. Using fd69:6666:: only sets the network part of the address.
Remember to change the netmask too!
This should be the result:

/etc/network/interfaces

auto eth0
iface eth0 inet6 static
address fd69::6666
netmask 64
  • Remarkably enough, radvd is not really needed. Perhaps because i didn't add the autoconf 0 clause? – ppparadox Nov 13 '15 at 15:52
  • The Debian machine now lost its global IPv6 address. How can this be? – ppparadox Nov 13 '15 at 16:11
  • I would stick to 64 bit netmask. – Archemar Nov 13 '15 at 16:13
  • Why? Is it related to the debian machine losing its global address? – ppparadox Nov 13 '15 at 16:18
  • For some reason now echo 1 > /proc/sys/net/ipv6/conf/eth0/autoconf is needed (plus waiting a few minutes). Add to sysctl.conf as needed. – ppparadox Nov 13 '15 at 16:52

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