Any reason why you want to replace the D6400?
If you are still on DSL internet your choices are limited.
The approach favoured by experienced users is to have a separate modem and router. That way you can wider choice of routers that a combination modem/router.
The ideal DSL modem from Netgear is the DM200.
The bad news is that Netgear, and most other brands, seem to have abandoned the market for DSL devices, modems and modem/routers.
If you can lay your hands on something like the DM200, that would be a good choice. But the prices are getting silly. You may be able to find a second-hand one. I bought one from one of those "open box" merchants. It looked new, with all the usual packing and protection.
You can run your your modem/router in modem-only mode, but, as I found, that can cause problems.
