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diff --git a/custom/topo-2sw-2host.py b/custom/topo-2sw-2host.py
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+"""Custom topology example
+
+Two directly connected switches plus a host for each switch:
+
+   host --- switch --- switch --- host
+
+Adding the 'topos' dict with a key/value pair to generate our newly defined
+topology enables one to pass in '--topo=mytopo' from the command line.
+"""
+
+from mininet.topo import Topo
+
+class MyTopo( Topo ):
+    "Simple topology example."
+
+    def __init__( self ):
+        "Create custom topo."
+
+        # Initialize topology
+        Topo.__init__( self )
+
+        # Add hosts and switches
+        leftHost = self.addHost( 'h1' )
+        rightHost = self.addHost( 'h2' )
+        leftSwitch = self.addSwitch( 's3' )
+        rightSwitch = self.addSwitch( 's4' )
+
+        # Add links
+        self.addLink( leftHost, leftSwitch )
+        self.addLink( leftSwitch, rightSwitch )
+        self.addLink( rightSwitch, rightHost )
+
+
+topos = { 'mytopo': ( lambda: MyTopo() ) }