Configuring a LAN

By default, IPMininet uses IPSwitch to create regular switches (not Openflow switches) and hubs. The switches use the Spanning Tree Protocol by default to break the loops. The hubs are switches that do not maintain a MAC address table and always broadcast any received frame on all its interfaces.

Here is an example of a LAN with a few switches and one hub.

from ipmininet.iptopo import IPTopo

class MyTopology(IPTopo):

    def build(self, *args, **kwargs):

        # Switches
        s1 = self.addSwitch("s1")
        s2 = self.addSwitch("s2")
        s3 = self.addSwitch("s3")
        s4 = self.addSwitch("s4")

        # Hub
        hub1 = self.addHub("hub1")

        # Links
        self.addLink(s1, s2)
        self.addLink(s1, hub1)
        self.addLink(hub1, s3)
        self.addLink(hub1, s4)

        super(MyTopology, self).build(*args, **kwargs)

The Spanning Tree Protocol can be configured by changing the `stp_cost` on the links (or directly on each interface). The default cost is 1.

from ipmininet.iptopo import IPTopo

class MyTopology(IPTopo):

    def build(self, *args, **kwargs):

        # Switches
        s1 = self.addSwitch("s1")
        s2 = self.addSwitch("s2")
        s3 = self.addSwitch("s3")
        s4 = self.addSwitch("s4")

        # Hub
        hub1 = self.addHub("hub1")

        # Links
        self.addLink(s1, s2, stp_cost=2)  # Cost changed for both interfaces
        self.addLink(s1, hub1)
        ls3 = self.addLink(hub1, s3)
        ls3[s3].addParams(stp_cost=2)  # Cost changed on a single interface
        self.addLink(hub1, s4)

        super(MyTopology, self).build(*args, **kwargs)

In the Spanning Tree Protocol, each switch has a priority. The lowest priority switch becomes the root of the spanning tree. By default, switches declared first have a lower priority number. You can manually set this value when you create the switch.

from ipmininet.iptopo import IPTopo

class MyTopology(IPTopo):

    def build(self, *args, **kwargs):

        # Switches with manually set STP priority
        s1 = self.addSwitch("s1", prio=1)
        s2 = self.addSwitch("s2", prio=2)
        s3 = self.addSwitch("s3", prio=3)
        s4 = self.addSwitch("s4", prio=4)

        # Hub
        hub1 = self.addHub("hub1")

        # Links
        self.addLink(s1, s2, stp_cost=2)  # Cost changed for both interfaces
        self.addLink(s1, hub1)
        ls3 = self.addLink(hub1, s3)
        ls3[s3].addParams(stp_cost=2)  # Cost changed on a single interface
        self.addLink(hub1, s4)

        super(MyTopology, self).build(*args, **kwargs)