I find that my router waits until the entire lease time passes before renewing, but when I power up my CentOS VM with a dhcp server running and I connect it to the WAN port on my router, my router will follow RFC guidelines and renew when half of the lease time passes. My question is what is my ISP's dhcp server doing to have my router wait until the lease expires before renewing?

It's the router that's not renewing the WAN connection in the right intervals when it obtains a lease from the ISP (waiting up until the lease expires to renew). I was using CentOS as a dhcp service (not client) to figure out if it was an issue with the router itself or is it something the ISP's dhcp server is doing that's telling my router to wait the entire lease before renewing(When I did this scenario the router only waited until half of the lease time passed before renewing, as it should.)

But why does it comply with RFC when I set it up to obtain a lease from the dhcp service on my CentOS virtual machine? That's what's puzzling me.

FYI, the ISP did not provide me with the router.