Re: DLINK DSL-3782 bridge/modem mode
For reference, just in case it might be helpful to others:
I switched off the Talktalk router. Connected a laptop to the Asus via network cable. Set the Asus to router only as described here:
https://www.asus.com/my/support/FAQ/1016292/
Then switched off the Asus, connected to the TalkTalk router via a network cable, followed the steps in the screenshots a few posts above, switched off wifi on the TalkTalk router.
Finally, I connected the TT and the Asus via cable - note the cable must go in the specific port specified when setting up the Asus as router only.
It all worked fine, except there was no internal DNS: \\mynas no longer found the NAS, but connecting to the specific IP address of the NAS worked. Most home users do not have a NAS or similar device whose name needs to be resolved, so they wouldn't even notice.
I followed the steps described here:
https://unfinishedbitness.info/2015/05/26/asuswrt-finalized-setup/
to set the internal DNS (LAN on the left bar of the Asus menu -> DHCP and DNS on the right) to the IP of the router (in my case, 192.168.1.1) and it all worked fine.
Oh, I also set the WAN DNS to Google's , so Talk Talk can no longer hijack the page if an address is wrong.