How works the "default fanout" in mininet?

Question

I read that "fanout" is the number of downstream links on each virtual switch. But, what happens with a default fanout, how many downstream links it will creat?. For example, in the below mininet command, what is the result?

sudo mn --topo tree,depth=3

Answer 1

Checking the topolib.py code of Mininet on github, by default fanout is equal to 2. So it will create a binary tree.

class TreeTopo( Topo ):
    "Topology for a tree network with a given depth and fanout."

    def build( self, depth=1, fanout=2 ):
        # Numbering:  h1..N, s1..M
        self.hostNum = 1
        self.switchNum = 1
        # Build topology
        self.addTree( depth, fanout )