The NIST standard FF3 scheme (also known as BPS scheme) is a tweakable block cipher based on a 8-round Feistel Network. We break it with a practical attack. Our attack exploits the bad domain separation in FF3 design. The attack works with chosen plaintexts and tweaks when the message domain is small. Our FF3 attack requires $O(N^{\frac{11}{6}})$ chosen plaintexts with time complexity $N^{5}$, where $N^2$ is domain size to the Feistel Network. Due to the bad domain separation in 8-round FF3, we reduced the FF3 attack to an attack on 4-round Feistel Networks. In our generic attack, we reconstruct the entire codebook of 4-round Feistel Network with $N^{\frac{3}{2}} \left( \frac{N}{2} \right)^{\frac{1}{6}}$ known plaintexts and time complexity $N^{4}$.