Region : UnitedKingdom

Model : TL-WDR4300

Hardware Version : V1

Firmware Version :

ISP :

TP-Link TD-W8980 - won't feed secondary router running DD-WRT

I am replacing my old SMC adsl router with the TP-Link TD-W8980 - and have set up the TD-W8980 without problem!
So I have wifi 2.4/5G and cable connection to my computer - all OK
BUT - my old router connected to a secondary router running DD-WRT - which works perfectly!
However when I connect the secondary router to the TP-Link TD-W8980 - I get no internet access from the DD-WRT router!
But if I connect my computer to the same ethernet cable, there is full internet access
So my question is:-

Since I have changed nothing in the working secondary DD-WRT router - is there anything in the TP-Link TD-W8980 setup that I have to modify to correct the problem? - is there anything in the TD-W8980 blocking access from the secondary router?


Advice appreciated please