Provide DHCP to devices on secondary (extension) router

[Swamp Thing]

I have connected a second router to my ISP's router using a LAN cable in order to cover areas that the ISP's WiFi doesn't reach too well.

The first router's IP is 192.168.xy.1, and I set the second router to be 192.168.xy.7. Now if I connect to the second router's WiFi I can use the internet from my devices. The problem is that the second router can provide only IPv6 automatically; if I want IPv4 then I have to use a static IP because the second router has DHCP disabled as per recommendations that I found online.

My question is: Can it work if I enable DHCP on the second router? If not, can the first router's DHCP service be made available to devices that connect to the second router?

 

[Swamp Thing]

After some online research I enabled DHCP on both routers, setting up non-overlapping pools of addresses. So devices can get connected via either router.

However, the secondary router still doesn't know how to forward IPV4 internet traffic to the first one. (IPV6 somehow works magically, maybe it has built in smartness to find routes). I will post a separate question about routing.

I may mention that the secondary router is actually an old ISP-provided fiber modem/router, so maybe its firmware doesn't allow DHCP discovery to pass through. Also it may need special configuration to make it recognize that the LAN1 port leads to the internet.