Fedora – Stable IPv6 address on Fedora

fedoraipv6

Unlike other systems, Fedora 25 workstation doesn't use stable IPv6 addresses, by default.

For example, with CentOS 7 or Fedora 23, a stable IPv6 is automatically configured (in an IPv6 enabled network where a IPv6 router is present) – i.e. one that is derived from the MAC-address.

That IPv6 address then can be used in an DNS AAAA-record.

In contrast to that, the IPv6 address of a Fedora 25 workstation system doesn't have any relation to its MAC address and doesn't seem to be stable.

How to configure deterministic and stable IPv6 addresses on Fedora 25?

Best Answer

On Fedora 25 Workstation, NetworkManager (NM) configures all network interfaces, by default. That means also the wired ones. And the NetworkManager doesn't create EUI-64 derived IPv6 addresses. Instead it generates so called 'stable-privacy' ones. Apparently to not disclose the MAC address to each IPv6 destination.

This can be changed for a given interface $i via changing the IPV6_ADDR_GEN_MODE key in the /etc/sysconfig/network-scripts/ifcfg-$i configuration file. For example via:

sed -i 's/^IPV6_ADDR_GEN_MODE=stable-privacy/IPV6_ADDR_GEN_MODE=eui64/' \
  /etc/sysconfig/network-scripts/ifcfg-$i

The change is effective after NetworkManager rereads its configuration and after a reconnect:

nmcli con reload
nmcli con down $i
nmcli con up $i

Notes

  • this option isn't exposed via the NM settings GUI
  • the interface configuration files under /etc/sysconfig/network-scripts read by NM are Fedora/Redhat specific, but the configuration key is not - i.e. on other distributions NM just reads the interface configurations from different locations/configuration files

Fedora also comes with systemd-networkd which doesn't disable EUI64 generation, by default. Thus, a simpler way to get stable IPv6 addresses under Fedora is just to remove NetworkManager and configure/enable systemd-networkd, instead.

Or one can set the interface in question to unmanaged in NetworkManager and then configure it in systemd-networkd.

In any case, the networkd config is pretty minimal then, e.g.:

cat /etc/systemd/network/20-wired.network
[Match]
# manage all matching interfaces
#Name=en*
# just manage one:
Name=eno1
    
[Network]
DHCP=ipv4
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