Lately I’ve been messing with my home network - long story short I ended up buying new router because my old Buffalo WZR-HP-G300NH was starting to having problems with wifi signal strength out of the blue. So I ended up with NetGear N300 v2 running Tomato by Shibby and a smaller one TP-LINK WR710N for the other room. And here is the kicker - none of routers was able to obtain IP address on WAN port via DHCP (after cloning mac address of wan port, as mac was filtered by my Internet provided).

I tried different configurations, different firmwares, but it seems like only my Buffalo (running OpenWRT) was working fine. After wasting hours and reading many forums I decided to check default udhcpc settings on OpenWRT very next morning and there I had epiphany - Tomato used different configuration, and to be exact two options were missing:

My solution:

I hope this tip will save some time for some lost souls like me ;).