@Kauban This looks like a limitation of the UDM Pro. I was able to get this working without any issues using an OpenWRT router. The OpenWRT device does client side translation (CLAT) for IPv4. Also, all clients get assigned IPv6 addresses from the Jio IPv6 prefix.
If you set the Huawei CPE in bridge mode, connect the Huawei CPE to a WAN port on the UDM Pro with type DHCPv6. This should assign an IPv6 address to the UDM Pro WAN interface. Does this not happen? Now if the UDM Pro allows, it should be able to extend the received prefix to your other client devices. This should give you IPv6 connectivity and also DNS based IPv4 connectivity with DNS64 resolvers.
On OpenWRT in retrospect, is a simple config for this to work.
For IPv4 connectivity you'd need the UDM Pro to support CLAT, but doesn't look like it does. Otherwise you can introduce another router in between which does CLAT (OpenWRT preferably), however this would need to be a decent router which can provide 1 Gbps+ throughput.
If you set the Huawei CPE in bridge mode, connect the Huawei CPE to a WAN port on the UDM Pro with type DHCPv6. This should assign an IPv6 address to the UDM Pro WAN interface. Does this not happen? Now if the UDM Pro allows, it should be able to extend the received prefix to your other client devices. This should give you IPv6 connectivity and also DNS based IPv4 connectivity with DNS64 resolvers.
On OpenWRT in retrospect, is a simple config for this to work.
For IPv4 connectivity you'd need the UDM Pro to support CLAT, but doesn't look like it does. Otherwise you can introduce another router in between which does CLAT (OpenWRT preferably), however this would need to be a decent router which can provide 1 Gbps+ throughput.
