Setup interface for ip6ip6 tunneling

Running into systemd-networkd bugs, don't be fooled by "Local=::1" and
"Remote=::1". This still results in the equivalent of setting them to
'any' or '::' because we are using the default interface name.

global/overlay/etc/puppet/modules/cdn/manifests/cache.pp

@@ -71,6 +71,22 @@ class cdn::cache(
     content => template('cdn/cache/10-cdn-ipip.network.erb'),
   }
 
+  file { '/etc/systemd/network/10-cdn-ip6tunl.netdev.erb':
+    ensure  => file,
+    owner   => 'root',
+    group   => 'root',
+    mode    => '0644',
+    content => template('cdn/cache/10-cdn-ip6tunl.netdev.erb'),
+  }
+
+  file { '/etc/systemd/network/10-cdn-ip6tunl.network.erb':
+    ensure  => file,
+    owner   => 'root',
+    group   => 'root',
+    mode    => '0644',
+    content => template('cdn/cache/10-cdn-ip6tunl.network.erb'),
+  }
+
   # Reload the network config if it has changed
   exec { 'networkctl reload':
     subscribe   => [File['/etc/systemd/network/10-cdn-dummy.network'], File['/etc/systemd/network/10-cdn-ipip.network']],

global/overlay/etc/puppet/modules/cdn/templates/cache/10-cdn-ip6tunl.netdev.erb

@@ -0,0 +1,16 @@
+[NetDev]
+Name=ip6tnl0
+Kind=ip6tnl
+
+[Tunnel]
+Independent=true
+# Local and Remote should be 'any' or '::' but right now it does not work.
+# However, by using the name "ip6tnl0" that matches the name of the interface
+# automatically created when the kernel module is loaded it seems we can set
+# anything "non-zero" here and the config will be accepted but still leaving
+# "::" as both Local and Remote on the interface. This then results in the
+# wanted configuration for now. One bug cancelling out another bug?
+# https://github.com/systemd/systemd/issues/34930
+Local=::1
+Remote=::1
+Mode=ip6ip6

global/overlay/etc/puppet/modules/cdn/templates/cache/10-cdn-ip6tunl.network.erb

@@ -0,0 +1,2 @@
+[Match]
+Name=ip6tnl0