Mininet簡介

在Coursera SDN開放課程中，編程作業要用Mininet來完成。這里對Mininet做一個簡單的介紹。 

什么是Mininet

       Mininet是由一些虛擬的終端節點（end-hosts）、交換機、路由器連接而成的一個網絡仿真器，它采用輕量級的虛擬化技術使得系統可以和真實網絡相媲美。

       Mininet可以很方便地創建一個支持SDN的網絡：host就像真實的電腦一樣工作，可以使用ssh登錄，啟動應用程序，程序可以向以太網端口發送數據包，數據包會被交換機、路由器接收並處理。有了這個網絡，就可以靈活地為網絡添加新的功能並進行相關測試，然后輕松部署到真實的硬件環境中。

Mininet的特性

       可以簡單、迅速地創建一個支持用戶自定義的網絡拓撲，縮短開發測試周期

       可以運行真實的程序，在Linux上運行的程序基本上可以都可以在Mininet上運行，如Wireshark

       Mininet支持Openflow，在Mininet上運行的代碼可以輕松移植到支持OpenFlow的硬件設備上

       Mininet可以在自己的電腦，或服務器，或虛擬機，或者雲（例如Amazon EC2）上運行

       Mininet提供python API，簡單易用

       Mininet是開源項目，源代碼在這里：https://github.com/mininet

       ……

Mininet安裝

       使用VirtualBox安裝Mininet虛擬機：http://mininet.org/download/

使用Mininet創建一個網絡

　　以Coursera SDN Week3 programming assignment為例，創建一個及其簡單的數據中心網絡。

　　Data center networks typically have a tree-like topology. End-hosts connect to top-of-rack switches, which form the leaves (edges) of the tree; one or more core switches form the root; and one or more layers of aggregation switches form the middle of the tree. In a basic tree topology, each switch (except the core switch) has a single parent switch. Additional switches and links may be added to construct more complex tree topologies (e.g., fat tree) in an effort to improve fault tolerance or increase inter-rack bandwidth.

　　In this assignment, your task is to create a simple tree topology. You will assume each level i.e., core, aggregation, edge and host to be composed of a single layer of switches/hosts with a configurable fanout value (k) looks like: 

　　代碼：

# CustomTopo.py
'''
Coursera:
- Software Defined Networking (SDN) course
-- Module 3 Programming Assignment

Professor: Nick Feamster
Teaching Assistant: Muhammad Shahbaz
'''

from mininet.topo import Topo
from mininet.net import Mininet
from mininet.node import CPULimitedHost
from mininet.link import TCLink
from mininet.util import irange,dumpNodeConnections
from mininet.log import setLogLevel

class CustomTopo(Topo):
    "Simple Data Center Topology"

    "linkopts - (1:c1, 2:aggregation, 3: edge) parameters"
    "fanout - number of child switch per parent switch"
    def __init__(self, linkopts1, linkopts2, linkopts3, fanout=2, **opts):
        # Initialize topology and default options
        Topo.__init__(self, **opts)
                        
        # Add your logic here ...
        self.fanout = fanout
        core = self.addSwitch('c1')
        for i in irange(1, fanout):
            aggregation = self.addSwitch('a%s' %i)
            self.addLink(core, aggregation, **linkopts1)
            for j in irange(1, fanout):
                edge = self.addSwitch('e%s' %(fanout*(i-1)+j))
                self.addLink(aggregation, edge, **linkopts2)
                for k in irange(1, fanout):
                    host = self.addHost('h%s' %((fanout*(fanout*(i-1)+j-1))+k))
                    self.addLink(edge, host, **linkopts3)
                   
topos = { 'custom': ( lambda: CustomTopo() ) }

def simpleTest():
    "Create and test a simple network"
    linkopts1 = dict(bw=10, delay='3ms', use_htb=True)
    linkopts2 = dict(bw=8, delay='4ms', loss=1, max_queue_size=900, )
    linkopts3 = dict(bw=6, delay='5ms', loss=1, max_queue_size=800)
    topo = CustomTopo(linkopts1, linkopts2, linkopts3, fanout=2)
    net = Mininet(topo, host=CPULimitedHost, link=TCLink)
    net.start()
    print "Dumping host connections"
    dumpNodeConnections(net.hosts)
    print "Testing network connectivity"
    net.pingAll()
    net.stop()

if __name__ == '__main__':
   # Tell mininet to print useful information
   setLogLevel('info')
   simpleTest()

　　在mininet虛擬機上執行下面操作即可創建自定義的網絡拓撲。函數simpleTest()創建網絡並進行了簡單的ping測試，從屏幕輸出可以看到創建的過程。

　　　　mininet@mininet-vm:~/mininet$ sudo python CustomTopo.py

 

更多資料

1. Mininet: http://mininet.org/

2. Mininet wiki: https://github.com/mininet/mininet/wiki