@Burakkucat, the default gateway setting to accompany the netmask value in the LAN IP setup, which would be the address of the firebrick as it is the gateway to the internet, set on those two-mode LANs as 192.168.n.254 whereas the modem's admin i/f is set to 192.168.n.1 (see FB config snippets poss). The modem does not know how to reach nodes outside the subnet defined by the netmask, which is set to be a /24 arbitrarily. I think that is the thing stopping eg DNS, NTP etc from working in the modem.