ddns-scripts [nsupdate]: impossible to configure nsupdate with ipv6 without (a single) forced update

Maintainer: feckert
Environment: 21.02.1

Description:

It is impossible to configure ddns-scripts-nsupdate for IPv6 protocol so that no forced updates happen and the ip address is till checked at intervals. Also, a client can not be configured so that it is ran once without a forced update. This is because run-once is always enabled if and only if forced_interval=0. If forced_interval!=0, there will always be forced updates at the specified unit intervals. There is actually no way to disable forced updates! See: https://openwrt.org/docs/guide-user/services/ddns/client .

This is in conflict of nsupdate terms. They are very adamant on not updating the IP address if it has not been changed; from nsupdate.info documentation:

Note: please do not “update” your IP address if it did not change. Doing so is considered abusive use of the service. All sane dyndns2 clients only send an update if the IP address has changed.

Running the forced update when IP has not changed can cause an abuse flag to be enabled for the client.

Though, I'm not sure whether this will be an issue if the client sets a forced update, say, every 31th day. For cleanness sake, there should probably be a separate setting for run-once and no forced updates, although this workaround exists. There is no workaround for users who might want or need a run-once non-forced update.

EDIT2: Clarified my wording, it was not quite what the problem is.

Start by tracing the ddns-scripts-nsupdate configuration handling for forced_interval, run-once, and IPv6 checks, using the linked OpenWrt client documentation and nsupdate.info guidance as behavioral context. Done means IPv6 can be checked at intervals without forced updates, and a client can perform one non-forced run.