Old Vyatta/VyOS versions once had an official way to disable all IPv6, like set system ipv6 disable. We removed it because the agreement was that there are no valid cases for disabling IPv6 and we shouldn't have supported misguided ideas.

Linux still have an option to do that and people can try to set it in VyOS using the CLI for custom sysctl options: set system sysctl parameter net.ipv6.conf.all.disable_ipv6 value '1'.

However, there are many places in VyOS where we assume that IPv6 is available. As T7267 shows, attempts to disable IPv6 that way cause commit errors.

We need to decide if the idea to disable IPv6 is valid and either remove those assumptions of officially declare that it's unsupported.