I have read Adding a whole IPv6 /64 block to an network interface on debian We want to make use of the AnyIP feature to add a whole IPv6 /64 subnet block to a web hosting server but using Netplan because we are on Ubuntu 18.04

Side note: a couple of experts have advised against using AnyIP to configure IPv6 so we will also look at alternative solutions like manually configuring a smaller number of IPs.

Our datacenter does already route the /64 to a single IP, for example

The range  2001:db8:1:10::0/64  is routed to the IP  2001:db8:1::1:10
The range  2001:db8:1:11::0/64  is routed to the IP  2001:db8:1::1:11

In Netplan I can configure single IPs this way

  version: 2
  renderer: networkd
      accept-ra: no
        - '2001:db8:1::1:10/48'
        - '2001:db8:1:10::0/64'
        - '2001:db8:1:10::1/64'
      gateway6: '2001:db8:1::1'

And this works. However I want to use the whole 2001:db8:1:10::/64 range on this server and I don't want to configure it in 18446744073709551616 lines.

Executing this command makes me able to ping all the /64 IPs from outside:

ip -6 route add local 2001:db8:1:10::/64 dev lo

Side note: a server daemon needs to support IP_FREEBIND to be able to bind to an IP which is not explicitly configured on an interface.

My question is: instead of having to execute ip -6 route add local .. after each reboot I would like to configure it the proper way inside the Netplan Yaml config.

  • Why are you want a single host to have 18,446,744,073,709,551,616 addresses? Also, IPv6 allows you to use every address in s subnet, including the subnet address, so assigning 1aaa:2bbb:1:10::/64 to an interface is actually only assigning that single address to the interface, not the entire subnet. – Ron Maupin Oct 23 '18 at 18:42
  • @RonMaupin It is quite common practice to add a whole /64 subnet to a single web hosting server. This makes sure you will never ever run out of IP addresses on the server. I know adding 1aaa:2bbb:1:10::/64 only adds one IP being 1aaa:2bbb:1:10::0. The question is how to add the whole range at once. – Jeroen Vermeulen - MageHost Oct 23 '18 at 18:45
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    IP addresses for VMs and containers need to be assigned within the guest, not on the host. The host must route the addresses to the guest. – Michael Hampton Oct 23 '18 at 19:42
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    In that case you're just fine to route the whole block to lo. Just be aware of it if you do start hosting containers or VMs in future. – Michael Hampton Oct 23 '18 at 20:42

Found a solution, but maybe someone knows a better one?

cat <<EOF > /usr/lib/networkd-dispatcher/routable.d/50-ipv6-block
ip -6 route add local 2001:db8:1:10::/64 dev lo
exit 0

chmod 755 /usr/lib/networkd-dispatcher/routable.d/50-ipv6-block

To check if it works:

ip -6 route del local 2001:db8:1:10::/64
netplan apply
systemctl --no-pager status networkd-dispatcher.service
route -6 | grep 2001:db8:1:10::/64
ping6 -c2 2001:db8:1:10::1234

If you see a RTNETLINK answers: File exists this is because a route is added which already existed because of an earlier netplan apply

  • That is adding a route, not the addresses to a host. There is a big difference. Routing will send a packet to the network with the host having the destination address on a packet, but assigning an address to an interface means that the payload for a packet received on that interface will be handled by the network stack assigned to the interface. – Ron Maupin Oct 23 '18 at 20:22
  • My question is to use the AnyIP feature, and adding a route is the way to do that. – Jeroen Vermeulen - MageHost Oct 23 '18 at 20:30
  • "However I want to use the whole 2001:db8:1:10::/64 range on this server and I don't want to configure it in 18446744073709551616 lines." That would be assigning addresses to the host, and you are asking about assigning to the host, but you are actually adding a route on the host, not assigning the network to the host. Based on how you asked the question, it sounds like you are confused about how it works. It is routing the packets, not assigning addresses to the server. – Ron Maupin Oct 23 '18 at 20:34
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    @RonMaupin Routes of type local are special. The documentation for type local says this: the destinations are assigned to this host. The packets are looped back and delivered locally. So it really does behave like every one of the IPs in the range are assigned to the host. Only caveat is that applications have to set a socket option before being able to bind to them explicitly. (Sockets listening on :: will receive connections on every IP address in the range.) – kasperd Oct 23 '18 at 21:47
  • Since no other answer has shown up I am going to award the bounty to this one. If you are still looking for a better answer you can use that reputation to start a new bounty. – kasperd Nov 1 '18 at 20:28

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