Um, you have that router going into something else? My question to you is why are there two dhcp servers running on your network? looks like your WAN is being deauthenticated for some reason.
I think your server configuration is wrong. You wan is trying to auth with your server which it obtains an ip address as seen in the log. 192.168.100.2, but it looks like, from your logs, that you have not configured a DNS server or a DNS forwarder. The other discrepancy that I see here, that i'm getting from the logs is that it is quickly loosing that ip address, which I believe could only mean that the IP address is already in use. I see this because 1: it quickly looses it's lease and 2, the log shows it dropped a packet from 192.168.100.2. Meaning that the router is dropping it's own packet to itself, which is not possible and illogical. Once that local IP lease has been lost, it is authenticating with your ISP, the way it should be.