feistel cipher and number of rounds
There is a minimal number of rounds for theoretical security. 4 rounds are required to construct a strong pseudo random permutation (PRP) from a pseudo-random function (PRF).

In practice, cryptographers don't tend to design ciphers with a heavy PRF for the f-function but instead apply more rounds with a weaker f-function to get the requisite strength. 

For this reason, there is no typical or default choice for the number of rounds in a Fiestel cipher. The optimal choice depends entirely on the internal security properties of the key schedule and F-function for the specific cipher in question.