TL;DR: This article speaks about IPv6 Stateless Address Autoconfiguration (SLAAC) EUI64 mechanism

There are basically three ways to configure IPv6 on a Linux server:

  1. DHCPv6: This has been unreliable in my experience. By default, you cannot use the MAC address to create a static lease, and the UUID is difficult to find and is not static either.
  2. SLAAC: The Stateless Address Autoconfiguration method is essentially the default. On a server, though, I want a single, static, predictable address. Let’s cover that below.
  3. Manual: We can always configure the address manually. This is of course a valid option and there is nothing more to add about it.

Note: There is always link local address from the fe80::/10 subnet and that is fine.

2) SLAAC:

Systemd-Networkd

  1. Let’s first list our connections:
# networkctl
IDX LINK    TYPE     OPERATIONAL SETUP
  1 lo      loopback carrier     unmanaged
  2 ens18   ether    routable    configured
  3 podman0 bridge   routable    unmanaged
  1. The configuration part:
# /etc/systemd/network/20-ens18.network
[Match]
Name=ens18

[Network]
DHCP=ipv4
Token=eui64
IPv6AcceptRA=yes
IPv6PrivacyExtensions=no

The Token option sets which SLAAC mechanism will be used to generate the primary IPv6 address.

The IPv6PrivacyExtensions option controls whether additional dynamic IPv6 addresses will be assigned.

  1. Now we just need to restart the network. Make sure you have another way to access the machine!
# networkctl reload
# networkctl reconfigure ens18

NetworkManager

  1. Let’s first list our connections:
# nmcli con show
NAME     UUID                                  TYPE      DEVICE
ens18    711aee22-6717-3d36-871e-4b14478ca5f3  ethernet  ens18
lo       08efa8c5-780b-4a47-878d-1ef091fe9b32  loopback  lo
podman0  e6cf2685-25c7-464f-93d9-078f283cc37c  bridge    podman0
  1. The configuration part:
# nmcli con modify ens18 ipv6.method auto
# nmcli con modify ens18 ipv6.ip6-privacy disabled
# nmcli con modify ens18 ipv6.addr-gen-mode eui64

The ipv6.addr-gen-mode option sets which SLAAC mechanism will be used to generate the primary IPv6 address.

The ipv6.ip6-privacy option controls whether additional dynamic IPv6 addresses will be assigned.

  1. Now we just need to restart the network. Make sure you have another way to access the machine!
# nmcli con down ens18; nmcli con up ens18

Final thoughts

I like EUI64 because the IPv6 address is predictable. I don’t have to configure both DNS and the system manually — I just keep track of the NIC’s hardware address, and the only place I need to make changes is DNS. I’d like to use DHCPv6 static leases, but until that becomes reliable I’ll probably stick with this method.

linux  network