My modem router gives out an IP address via DHCP to my OpenWRT router (TP-Link WDR3600) via DHCP. The OpenWRT has an IP address, 192.168.3.2. The IP address of the modem router is 192.168.3.254.
The LAN of the OpenWRT router is 192.168.1.x.
How do I access the modem router at 192.168.3.254 when connected to the OpenWRT's LAN?