SDN控制器-POX學習（一）

本文實驗環境:
1.VirtualBox
2.SDN Hub tutorial VM 64bit

學習目標:
1.熟悉SDN Hub tutorial
2.學習POX提供的樣例代碼:tutorial_l2.hub.py

SDN Hub tutorial就不多介紹，官方的介紹如下:
All-in-one SDN App Development Starter VM
翻譯成中文就是一款集所有SDN相關APP的VM 鏡像,方便我這樣的初學者進行學習.

SDN Hub tutorial安裝很簡單，到官網下載最新的版本，導入到VirtualBox或者VMware這樣的虛擬機軟件.

一、下面是本次實驗的步驟了:

1.安裝SDN Hub tutorial
2.在命令行通過mininet創建一個網絡，該網絡具備三臺主機，一臺交換機和一個控制器。
具體命令如下:

$ sudo mn --topo single,3 --mac --controller remote --switch ovsk

sudo ovs-vsctl set bridge s1 protocols=OpenFlow10

3.啓動POX控制器，並使用tutorial_l2.hub.py這個模塊，這個模塊是用Python實現的集線器

cd /home/ubuntu/pox && ./pox.py log.level --DEBUG forwarding.tutorial_l2_hub

4.最後在mininet命令端輸入h1 ping h2,可以看到h1能夠ping通h2.

二.結果理解
1.tutorial_l2.hub.py程序

from pox.core import core
import pox.openflow.libopenflow_01 as of

class L2Hub (object):
    def __init__ (self, connection):
        # Keep track of the connection to the switch so that we can
        # send it messages!
        self.connection = connection

        # This binds all our event listener
        connection.addListeners(self)

    # Handles packet in messages from the switch.
    # 處理PackIn消息
    def _handle_PacketIn (self, event):
        packet = event.parsed # This is the parsed packet data.

        packet_in = event.ofp # The actual ofp_packet_in message.
        #生成packet_out消息
        msg = of.ofp_packet_out()
        msg.buffer_id = event.ofp.buffer_id
    msg.in_port = packet_in.in_port

        # Add an action to send to the specified port
        #講所有來到交換機的數據包都從其它端口轉發出去
        action = of.ofp_action_output(port = of.OFPP_FLOOD)
        msg.actions.append(action)

        # Send message to switch
        self.connection.send(msg)

def launch ():
    def start_switch (event):
        #實例化一個Hub
        L2Hub(event.connection)
    #添加監聽
    core.openflow.addListenerByName("ConnectionUp", start_switch)

2.數據包交互時序，以h1 ping h2爲例