DHCP-router is a TL-WR841N / TL-WR841ND. It hast built-in "SPI Firewall" that is enabled. I have forwarding roules on it that forward all ports to a certain IP. The WAN connection is connected to LAN of routerB. The WAN has a fixed IP in the IP-range of routerB. Set as default gateway is the IP of routerB.
There are settings for primary and secondary DNS servers on the DHCP-server, but they are greyed out. Primary would be the default gateway, meaning routerB. Secondary is labeled "optional" and now empty (0.0.0.0). I can set those by enabling "use these DNS servers". But since my internet connection is working fine from the PC, I dont think that the problem is located there.
System routing table of this DHCP-server-router shows three IDs:
1 Destination Network: 192.168.111.0 - subnet mask: 255.255.255.0 - gateway 0.0.0.0 -Interface: LAN & WAN
2 Destination Network: 192.168.555.0 (routerB IP range) - subnet mask: 255.255.255.0 - gateway 0.0.0.0 -Interface: WAN
3 Destination Network: 0.0.0.0 - subnet mask: 0.0.0.0 - gateway 192.168.555.303 (routerB IP) -Interface: WAN
I am not familiar with routing tables. The IPs of the table look okay, though.