Connect routers in series?

I’m attempting to configure a friend’s Omnia router ('B") by connecting it in series with my router (‘A’)–the WAN port of router B is connect to one of router A’s LAN ports.

Router A’s is on network 192.168.1.1 (mask: 255.255.255.0), while Router B’s is on network 192.168.3.1 (mask: 255.255.255.0). Router B’s address is assigned dynamically.

Once connected to one of router B’s two networks via wifi, I can access all of router B’s configuration interfaces (i.e. Foris, Luci, or ssh). Unfortunately, I can’t access the internet. When connect to router B via ssh, ping 217.115.15.26 (dev.openwrt.org) return network unreachable.

The problem appears to be with the WAN interface, but I’m not sure what I need to do next.