Exception Error in mininet

I have used Mininet to create a simple custom topology. It worked correctly When I was running it for the first time, but after that I received following error message:

Exception: Error creating interface pair (s1-eth1,h1-eth0): RTNETLINK answers: File exists

what is it and how can I solve it?

here is my topology:

from mininet.topo import Topo
from mininet.net import Mininet


class CustomTopo (Topo):

    def build(self):

        S1 = self.addSwitch('s1')

        H1 = self.addHost('h1')
        H2 = self.addHost('h2')

        self.addLink(S1, H1)
        self.addLink(S1, H2)


topo = CustomTopo()
net = Mininet(topo)
net.start()

topos = {'mytopo': CustomTopo}

and for more information I use Mininet 2.3.0d1

I run it by following command without remote controller and received another error: sudo mn --custom /home/bob/Desktop/Mtopo.py --topo=mytopo --mac

the error is: Exception: Please shut down the controller which is running on port 6653

I checked netstat -nl | grep 6653 but there is no active session on port 6653 and there is no other controller to shutdown.

Solution

You actually start Mininet twice. Once in your script and the other with the command line. Either change your script to:

from mininet.topo import Topo
from mininet.net import Mininet
from mininet.cli import CLI
from mininet.node import RemoteController

class CustomTopo (Topo):

    def build(self):

        S1 = self.addSwitch('s1')

        H1 = self.addHost('h1')
        H2 = self.addHost('h2')

        self.addLink(S1, H1)
        self.addLink(S1, H2)


topo = CustomTopo()
net = Mininet(topo, controller=lambda name: RemoteController(name, ip='127.0.0.1', protocol='tcp', port = 6633), autoSetMacs=True)
net.start()
CLI(net)
net.stop()

save to start_topology.py and run as

sudo python start_topology.run

or change your script to

from mininet.topo import Topo
from mininet.net import Mininet
from mininet.cli import CLI


class CustomTopo (Topo):

    def build(self):

        S1 = self.addSwitch('s1')

        H1 = self.addHost('h1')
        H2 = self.addHost('h2')

        self.addLink(S1, H1)
        self.addLink(S1, H2)


topo = CustomTopo()
topos = {'mytopo': CustomTopo}

save to mytopo.py and run as

sudo mn --custom mytopo.py --topo=mytopo --mac --controller=remote,ip=127.0.0.1,port=6633

(change the IP and PORT for your controller accordingly)