Tags for dynamic IPv6 prefixes

[SaarLAN-Pissbeutel]

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Is your feature request related to a problem? Please describe.

At the moment, it's not possible to insert a dynamic IPv6 host in any field in OPNsense allowing IP addresses, except for firewall rules, if an alias is used and set to the dynamic ipv6 host option.

This creates an issue if an IPv6 host is inserted in a field because at some point, the prefix offered by the provider will change and the entry would need updating. Good examples would be:

• creating an AAAA record in Unbound DNS
• using an IPv6 address for any service related entry in DHCP server, Router Advertisements and so on (e.g. the fields for DNS server, NTP server, ...)
• using IPv6 addresses or networks as parts of a VPN tunnel
• using an IPv6 address for firewall rules if an alias is not used

A feasible workaround in local networks is to use the link-local address. However, if the service should be reachable on other networks, the only possible way at the moment is to use ULA. This increases the complexity of the network since the (static) ULAs are only needed to talk to the hosts even though GUAs would be available. In addition, RFC6724 wants us to prefer IPv4 addresses (RFC1918 addresses included) over IPv6 ULA.

Describe the solution you like

A good solution would be to use tags like it is done already in the DynDNS plugin. There, the tags "__MYIP__" or "__HOSTNAME__" are used for custom URLs which are replaced internally.

Similarly, those tags could be used to insert the first 64 bits of the network in any field. The host part could be added thereafter creating a complete IPv6 address, e.g.:

• __IPV6NET:lan__::1:2:3:4
• __IPV6NET:opt1__::ffff
• __IPV6NET:opt2__::1

Additional context

A typical use-case would be:
Distributing the IPv6 address of another DNS service (e.g. Pihole, Adguard, Blocky, ...) via OPNsense DHCP/radvd to the clients in connected networks.