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@lantz lantz/gist:5640610
Last active Aug 12, 2019

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Script to set up NAT with Mininet
Example to create a Mininet topology and connect it to the internet via NAT
through eth0 on the host.
Glen Gibb, February 2011
(slight modifications by BL, 5/13)
from mininet.cli import CLI
from mininet.log import lg, info
from mininet.node import Node
from mininet.topolib import TreeNet
from mininet.util import quietRun
def startNAT( root, inetIntf='eth0', subnet='10.0/8' ):
"""Start NAT/forwarding between Mininet and external network
root: node to access iptables from
inetIntf: interface for internet access
subnet: Mininet subnet (default 10.0/8)="""
# Identify the interface connecting to the mininet network
localIntf = root.defaultIntf()
# Flush any currently active rules
root.cmd( 'iptables -F' )
root.cmd( 'iptables -t nat -F' )
# Create default entries for unmatched traffic
root.cmd( 'iptables -P INPUT ACCEPT' )
root.cmd( 'iptables -P OUTPUT ACCEPT' )
root.cmd( 'iptables -P FORWARD DROP' )
# Configure NAT
root.cmd( 'iptables -I FORWARD -i', localIntf, '-d', subnet, '-j DROP' )
root.cmd( 'iptables -A FORWARD -i', localIntf, '-s', subnet, '-j ACCEPT' )
root.cmd( 'iptables -A FORWARD -i', inetIntf, '-d', subnet, '-j ACCEPT' )
root.cmd( 'iptables -t nat -A POSTROUTING -o ', inetIntf, '-j MASQUERADE' )
# Instruct the kernel to perform forwarding
root.cmd( 'sysctl net.ipv4.ip_forward=1' )
def stopNAT( root ):
"""Stop NAT/forwarding between Mininet and external network"""
# Flush any currently active rules
root.cmd( 'iptables -F' )
root.cmd( 'iptables -t nat -F' )
# Instruct the kernel to stop forwarding
root.cmd( 'sysctl net.ipv4.ip_forward=0' )
def fixNetworkManager( root, intf ):
"""Prevent network-manager from messing with our interface,
by specifying manual configuration in /etc/network/interfaces
root: a node in the root namespace (for running commands)
intf: interface name"""
cfile = '/etc/network/interfaces'
line = '\niface %s inet manual\n' % intf
config = open( cfile ).read()
if ( line ) not in config:
print '*** Adding', line.strip(), 'to', cfile
with open( cfile, 'a' ) as f:
f.write( line )
# Probably need to restart network-manager to be safe -
# hopefully this won't disconnect you
root.cmd( 'service network-manager restart' )
def connectToInternet( network, switch='s1', rootip='10.254', subnet='10.0/8'):
"""Connect the network to the internet
switch: switch to connect to root namespace
rootip: address for interface in root namespace
subnet: Mininet subnet"""
switch = network.get( switch )
prefixLen = subnet.split( '/' )[ 1 ]
routes = [ subnet ] # host networks to route to
# Create a node in root namespace
root = Node( 'root', inNamespace=False )
# Prevent network-manager from interfering with our interface
fixNetworkManager( root, 'root-eth0' )
# Create link between root NS and switch
link = network.addLink( root, switch )
link.intf1.setIP( rootip, prefixLen )
# Start network that now includes link to root namespace
# Start NAT and establish forwarding
startNAT( root )
# Establish routes from end hosts
for host in network.hosts:
host.cmd( 'ip route flush root 0/0' )
host.cmd( 'route add -net', subnet, 'dev', host.defaultIntf() )
host.cmd( 'route add default gw', rootip )
return root
if __name__ == '__main__':
lg.setLogLevel( 'info')
net = TreeNet( depth=1, fanout=4 )
# Configure and start NATted connectivity
rootnode = connectToInternet( net )
print "*** Hosts are running and should have internet connectivity"
print "*** Type 'exit' or control-D to shut down network"
CLI( net )
# Shut down NAT
stopNAT( rootnode )
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