Ipv6 and wan ddns

The standard openwrt behavior seems to be assigning an GUA to lan interface and use it as the default ip for outgoing connections (prom the devices/scripts).

I'm trying to set openwrt to update dynamic dns record for the openwrt device and add firewall rules to allow connections to ssh on the device.

When I add the option to assign ipv6 GUA to WAN and use curl --interface option the outgoing connection is still made with lan's GUA (or at least that what the remote ddns server sets). Any idea how to change that behavior?

What DDNS provider and how it is configured?

In this particular case I'm testing a ipv6 lab (personal) machine and trying to recreate (or improve/upgrade) a rather complex setup using ipv4 (multiple subnets/vlans, vpn with selective access, multiple wans) and in many cases I'm having problems with the openwrt using lan's gua for outside connection… On the ddns front I've figured 2 possible workaround - 1. for those ddns services that have an api for it send wans gua in the message, and for those that don't curl --interface will work fine if I pass an ip rather then interface name.

I think I've figured out the problem - no default ipv6 route… openwrt configures routes based on delegated prefixes (good for multi-homing), but doesn't configure a default route. After adding a default route to the routing table the standard outgoing connection uses wan's GUA… Now I can't use lan's interface name (curl --interface lan ) to connect to the internet (using lan's gua works).