How do I create an IPv6 overlay network?

Question

I would like to create host-only IPv6 networks on two hosts and then route between them. On each host, there will be a dummy interface, at ipv6_prefix::9. I would like to be able to ping that interface from the other host.

Is there a well-developed best practice for this? It seems reasonable that one could do it with 6in4 tunnels.

Below, I'll work through the setup I tried recently in EC2, using 6in4 to tunnel. The two hosts are 10.239.143.35 and 10.238.249.113. First, let's set up the dummy interfaces. We'll use these Bash functions:

function dummy {
  local name="$1" ipv6="$2"
  ip link add "$name" type dummy
  ip -6 addr add "$ipv6" dev "$name"
  ip link set "$name" up
}

function calc6to4 {
  printf '2002:%02x%02x:%02x%02x::\n' $(tr '.' ' ' <<<"$@")
}

function eth0ipv4 {
  ip addr list dev eth0 | egrep -o 'inet [^/]+' | head -n1 | cut -d' ' -f2
}

(You can just paste these straight in to your shell session.)

On the first host, we run:

:;  ipv4="$(eth0ipv4)"
:;  ipv6="$(calc6to4 "$ipv4")"
:;  echo "ipv4 = $ipv4" "ipv6 = $ipv6"
ipv4 = 10.239.143.35 ipv6 = 2002:0aef:8f23::
:;  dummy dummy9 "$ipv6"9
:;  ip addr show dev dummy9
69: dummy9: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN 
    link/ether e2:69:75:10:04:2c brd ff:ff:ff:ff:ff:ff
    inet6 2002:aef:8f23::9/128 scope global 
       valid_lft forever preferred_lft forever
    inet6 fe80::e069:75ff:fe10:42c/64 scope link 
       valid_lft forever preferred_lft forever

Pinging seems to work okay:

:;  ping6 -q -c1 "$ipv6"9
PING 2002:0aef:8f23::9(2002:aef:8f23::9) 56 data bytes

--- 2002:0aef:8f23::9 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.040/0.040/0.040/0.000 ms

Now it's on to the second host:

:;  ipv4="$(eth0ipv4)"
:;  ipv6="$(calc6to4 "$ipv4")"
:;  echo "ipv4 = $ipv4" "ipv6 = $ipv6"
ipv4 = 10.238.249.113 ipv6 = 2002:0aee:f971::
:;  dummy dummy9 "$ipv6"9

Ping check checks out:

:;  ping6 -q -c1 "$ipv6"9
PING 2002:0aee:f971::9(2002:aee:f971::9) 56 data bytes

--- 2002:0aee:f971::9 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.037/0.037/0.037/0.000 ms

Now it's time for the exciting bit: connecting the hosts with 6in4 tunnels. We use the following Bash function on both hosts:

function tunnel {
  local name="$1" self_ipv4="$2" ipv4="$3" ipv6="$4"
  ip tunnel add "$name" mode sit ttl 64 remote "$ipv4" local "$self_ipv4"
  ip -6 addr add "$ipv6"1 dev "$name"
  ip -6 route add "$ipv6"/64 dev "$name" metric 1
  ip link set "$name" up
}

On the first host:

################################### IPv4 and IPv6 from host 2 ##
:;  tunnel tun6in4 10.239.143.35 10.238.249.113 2002:0aee:f971::

On the second:

################################### IPv4 and IPv6 from host 1 ##
:;  tunnel tun6in4 10.238.249.113 10.239.143.35 2002:0aef:8f23::

When we try to find a route from the first host to 2002:aee:f971::9, bound to the dummy device on the second, we get a hit:

:;  ip -6 route get 2002:aee:f971::9
2002:aee:f971::9 from :: dev tun6in4  src 2002:aee:f971::1  metric 0 
    cache 

But pings don't work:

:;  ping6 -q -c1 2002:aee:f971::9
PING 2002:aee:f971::9(2002:aee:f971::9) 56 data bytes

--- 2002:aee:f971::9 ping statistics ---
1 packets transmitted, 0 received, 100% packet loss, time 0ms

Maybe I need to add an address to eth0?

Answer 1

It turns out that the tunnel should have an IPv6 address on the source host, not the target host (the peer), for this simple ping test to work.

function tunnel {
  local name="$1" self_ipv4="$2" self_ipv6="$3" ipv4="$4" ipv6="$5"
  ip tunnel add "$name" mode sit ttl 64 remote "$ipv4" local "$self_ipv4"
  ip -6 addr add "$self_ipv6"1 dev "$name"
  ip -6 route add "$ipv6"/64 dev "$name" metric 1
  ip link set "$name" up
}

The tunnel setup commands would then be:

:;  tunnel tun6in4 10.239.143.35 2002:0aef:8f23:: 10.238.249.113 2002:0aee:f971::
:;  tunnel tun6in4 10.238.249.113 2002:0aee:f971:: 10.239.143.35 2002:0aef:8f23::