Easy libvirt IPv6 routed network

This is a tutorial on how to create a routed IPv6 libvirt network for testing. Having a “default” NAT network, create a new one called “isolated” as isolated network (no upstream connectivity). Then create new VM with two network cards both in “default” and “isolated” networks. I used CentOS 8.0 but this would work with any distribution.

First off, create new account at https://www.tunnelbroker.net and you will be given an IPv6 network:

  • Routed /64: 2001:db8:6f:443::/64
  • Routed /48: 2001:db8:59ef::/48
  • Server IPv6 Address: 2001:db8:6e:443::1/64
  • Client IPv6 Address: 2001:db8:6e:443::2/64

Delete automatically created connections:

	nmcli c delete enp1s0
	nmcli c delete "Wired connection 1"

Create upstream IPv4 connection, in my case it’s DHCP. Upstream is the interface connected to “default” NAT network:

	nmcli con add type ethernet con-name upstream ifname enp1s0 ipv6.method ignore

For downstream (connected to “isolated” network) use the “Routed /48” subnet, I’ve decided to resevre 8 bits making it /64 creating subnet with “cafe” octets. Make sure the connection is put into “trusted” zone when using firewalld, otherwise create rules to allow traffic from downstream hosts.

	nmcli c add con-name downstream type ethernet ifname enp2s0 ip6 2001:db8:59ef:cafe::1/64 connection.zone trusted

I haven’t looked into how to create 6in4 tunnel via Network Manager, so I used simple approach which can be found in Example Configurations on the tunnelbroker.net site:

	# cat /etc/rc.local 
	#!/bin/bash
	nm-online
	IP=$(nmcli -t -f IP4.ADDRESS con show upstream | cut -f2 -d: | cut -f1 -d/)
	ip tunnel add he-ipv6 mode sit remote 216.66.86.122 local $IP ttl 255
	ip link set he-ipv6 up
	ip addr add 2001:db8:6e:443::2/64 dev he-ipv6
	ip route add ::/0 dev he-ipv6

	cat >/etc/resolv.conf <<EOF
	nameserver 2001:db8:20::2
	EOF

	sysctl -w net.ipv6.conf.all.forwarding=1

	touch /var/lock/subsys/local

Remember to make it executable:

	# chmod +x /etc/rc.local

Run the script to create the tunnel and override the upstream DNS server. IPv6 communication should work now:

	# ping6 ipv6.google.com

For my testing purposes, RADVD with DNS advertisment should be enough:

	yum -y install radvd

Configuration is pretty simple, make sure to modify the subnet and interface name:

	# cat /etc/radvd.conf
	interface enp2s0
	{
					AdvSendAdvert on;
					AdvLinkMTU 1480;
					MaxRtrAdvInterval 300;
					prefix 2001:db8:59ef:cafe::/64
					{
									AdvOnLink on;
									AdvAutonomous on;
					};
					RDNSS 2001:db8:20::2 {
									AdvRDNSSLifetime 600;
					};
	};

Start the service, clients should be able to get IPv6 from the assigned subnet:

	systemctl enable --now radvd

That’s all actually, boot a VM in the “isolated” network. Most distributions will attempt to acquire an IPv6 addres and everything should work as expected.

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