Add bridges s1-s3 to topology and explain some details

examples/linuxrouter.py

@@ -6,20 +6,23 @@ linuxrouter.py: Example network with Linux IP router
 This example converts a Node into a router using IP forwarding
 already built into Linux.
 
-The topology contains a router with three IP subnets:
+The example topology creates a router and three IP subnets:
- - 192.168.1.0/24 (interface IP: 192.168.1.1)
- - 172.16.0.0/12 (interface IP: 172.16.0.1)
- - 10.0.0.0/8 (interface IP: 10.0.0.1)
 
- It also contains three hosts, one in each subnet:
+    - 192.168.1.0/24 (r0-eth1, IP: 192.168.1.1)
- - h1 (IP: 192.168.1.100)
+    - 172.16.0.0/12 (r0-eth2, IP: 172.16.0.1)
- - h2 (IP: 172.16.0.100)
+    - 10.0.0.0/8 (r0-eth3, IP: 10.0.0.1)
- - h3 (IP: 10.0.0.100)
 
- Routing entries can be added to the routing tables of the
+Each subnet consists of a single host connected to
- hosts or router using the "ip route add" or "route add" command.
+a single switch:
- See the man pages for more details.
 
+    r0-eth1 - s1-eth1 - h1-eth0 (IP: 192.168.1.100)
+    r0-eth2 - s2-eth1 - h2-eth0 (IP: 172.16.0.100)
+    r0-eth3 - s3-eth1 - h3-eth0 (IP: 10.0.0.100)
+
+The example relies on default routing entries that are
+automatically created for each interface. Additional
+routes may be added to the router or hosts by executing
+'ip route' or 'route' commands on the router or hosts.
 """
 
 from mininet.topo import Topo
@@ -42,29 +45,39 @@ class LinuxRouter( Node ):
 
 
 class NetworkTopo( Topo ):
-    "A simple topology of a router with three subnets (one host in each)."
+    "A LinuxRouter connecting three IP subnets"
 
     def build( self, **_opts ):
-        router = self.addNode( 'r0', cls=LinuxRouter, ip='192.168.1.1/24' )
+
+        defaultIP='192.168.1.1/24'  # IP address for r0-eth1
+        router = self.addNode( 'r0', cls=LinuxRouter, ip=defaultIP )
+
+        s1, s2, s3 = [ self.addSwitch( s ) for s in 's1', 's2', 's3' ]
+
+        self.addLink( s1, router, intfName2='r0-eth1',
+                      params2={ 'ip' : defaultIP } )  # for clarity
+        self.addLink( s2, router, intfName2='r0-eth2',
+                      params2={ 'ip' : '172.16.0.1/12' } )
+        self.addLink( s3, router, intfName2='r0-eth3',
+                      params2={ 'ip' : '10.0.0.1/8' } )
+
         h1 = self.addHost( 'h1', ip='192.168.1.100/24',
                            defaultRoute='via 192.168.1.1' )
         h2 = self.addHost( 'h2', ip='172.16.0.100/12',
                            defaultRoute='via 172.16.0.1' )
         h3 = self.addHost( 'h3', ip='10.0.0.100/8',
                            defaultRoute='via 10.0.0.1' )
-        self.addLink( h1, router, intfName2='r0-eth1',
+
-                      params2={ 'ip' : '192.168.1.1/24' } )
+        for h, s in [ (h1,s1), (h2,s2), (h3,s3) ]:
-        self.addLink( h2, router, intfName2='r0-eth2',
+            self.addLink( h, s )
-                      params2={ 'ip' : '172.16.0.1/12' } )
+
-        self.addLink( h3, router, intfName2='r0-eth3',
-                      params2={ 'ip' : '10.0.0.1/8' } )
 
 def run():
     "Test linux router"
     topo = NetworkTopo()
-    net = Mininet( topo=topo, controller=None )  # no controller needed
+    net = Mininet( topo=topo )  # controller is used by s1-s3
     net.start()
-    info( '*** Routing Table on Router\n' )
+    info( '*** Routing Table on Router:\n' )
     print net[ 'r0' ].cmd( 'route' )
     CLI( net )
     net.stop()