Maybe an option (for testing only) to try @Grisu suggestion of GNUton firmware on your DSL-AC68U as it is built in part using ASUSWRT-Merlin firmware. hopefully GNUtons build has included the DDNS option for Double NAT
Then this should be a good indication if this option will support DDNS and a good reference to others also in this dilemma.
I have not tried DDNS behind double NAT, maybe others on this forum have ?
In a completely sane world, madness is the only freedom (J.G.Ballard).
Necessary cookies are absolutely essential for the website to function properly. This category only includes cookies that ensures basic functionalities and security features of the website. These cookies do not store any personal information.
Any cookies that may not be particularly necessary for the website to function and is used specifically to collect user personal data via analytics, ads, other embedded contents are termed as non-necessary cookies. It is mandatory to procure user consent prior to running these cookies on your website.