Fedora CoreOS nodes do not get an IPv6 address in PDC
VMs created with Fedora CoreOS (FCOS) in the PDC manage to obtain an IP address from DHCP4, but not via DHCP6.
This happens due to the IPv6 address generate mode (NetworkManager setting ipv6.addr-gen-mode) which configures the method for creating the IPv6 interface identifer of addresses with RFC4862 IPv6, the permitted values are: "eui64" (0), "stable-privacy" (1), "default" (3) or "default-or-eui64" (2).
Fedora CoreOS defaults to "stable-privacy", which partially randomizes the interface identifier.
Instead we want "eui64" so NetworkManager simply uses the assigned IPv6 addresses and the VM will have a predictable IPv6 address that the hypervisor can route traffic to.
See INC4000735 and https://github.com/coreos/fedora-coreos-tracker/issues/513
AlmaLinux 9 VMs are not affected by the same issue.
The FCOS NetworkManager config can be adjusted with the following drop-in:
# /etc/NetworkManager/conf.d/90-dhcp.conf
[connection]
ipv6.addr-gen-mode=0(Tested with Fedora CoreOS 39.20240210.3.0 and NetworkManager 1.44.2-1.fc39)