【Openflow Tutorial】Create a learning switch

Openflow Tutorial: Create a learning switch

Github: https://github.com/mininet/openflow-tutorial/wiki

选择POX作为远程控制器，编写python程序实现交换机（Switch）功能，比较交换机（Switch）与集线器（Hub）的区别。

1.Switch VS Hub

Hub是将信号直接传输给所有其它端口，即传输线路是共享的；而Switch能够选择目标端口，在很大程度上减少冲突的发生，为通信双方提供了一条独占的线路。例如，对于mininet中的虚拟主机h1，h2，h3，若h1想要ping h2，则hub会将packet发送给h2与h3，而switch只会发送给h2。

2. Realize the function of Switch

要实现Switch功能，GitHub上下载的of_tutorial.py已经给出了较详细的注释说明，翻译成中文，其大致流程如下：
① 如果 目标端口未知：从packet中学习
② 如果 目标端口已知：发送packet；打印log信息；Match, Action, connection.send
③ 其他：向所有其他端口发送

# Copyright 2012 James McCauley
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at:
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""
This component is for use with the OpenFlow tutorial.

It acts as a simple hub, but can be modified to act like an L2
learning switch.

It's roughly similar to the one Brandon Heller did for NOX.
"""

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

log = core.getLogger()



class Tutorial (object):
  """
  A Tutorial object is created for each switch that connects.
  A Connection object for that switch is passed to the __init__ function.
  """
  def __init__ (self, connection):
    # Keep track of the connection to the switch so that we can
    # send it messages!
    self.connection = connection

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

    # Use this table to keep track of which ethernet address is on
    # which switch port (keys are MACs, values are ports).
    self.mac_to_port = {}


  def resend_packet (self, packet_in, out_port):
    """
    Instructs the switch to resend a packet that it had sent to us.
    "packet_in" is the ofp_packet_in object the switch had sent to the
    controller due to a table-miss.
    """
    msg = of.ofp_packet_out()
    msg.data = packet_in

    # Add an action to send to the specified port
    action = of.ofp_action_output(port = out_port)
    msg.actions.append(action)

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


  def act_like_hub (self, packet, packet_in):
    """
    Implement hub-like behavior -- send all packets to all ports besides
    the input port.
    """

    # We want to output to all ports -- we do that using the special
    # OFPP_ALL port as the output port.  (We could have also used
    # OFPP_FLOOD.)
    self.resend_packet(packet_in, of.OFPP_ALL)

    # Note that if we didn't get a valid buffer_id, a slightly better
    # implementation would check that we got the full data before
    # sending it (len(packet_in.data) should be == packet_in.total_len)).


  def act_like_switch (self, packet, packet_in):
    """
    Implement switch-like behavior.
    """

    """ # DELETE THIS LINE TO START WORKING ON THIS (AND THE ONE BELOW!) #

    # Here's some psuedocode to start you off implementing a learning
    # switch.  You'll need to rewrite it as real Python code.

    # Learn the port for the source MAC
    self.mac_to_port ... 

    if the port associated with the destination MAC of the packet is known:
      # Send packet out the associated port
      self.resend_packet(packet_in, ...)

      # Once you have the above working, try pushing a flow entry
      # instead of resending the packet (comment out the above and
      # uncomment and complete the below.)

      log.debug("Installing flow...")
      # Maybe the log statement should have source/destination/port?

      #msg = of.ofp_flow_mod()
      #
      ## Set fields to match received packet
      #msg.match = of.ofp_match.from_packet(packet)
      #
      #< Set other fields of flow_mod (timeouts? buffer_id?) >
      #
      #< Add an output action, and send -- similar to resend_packet() >

    else:
      # Flood the packet out everything but the input port
      # This part looks familiar, right?
      self.resend_packet(packet_in, of.OFPP_ALL)

    """ # DELETE THIS LINE TO START WORKING ON THIS #
    if packet.src not in self.mac_to_port:
      log.debug("Learned %s from Port %d!" % (packet.src, packet_in.in_port))
      self.mac_to_port[packet.src] = packet_in.in_port

    if packet.dst in self.mac_to_port:
      # Send packet out the associated port
      log.debug("CAM table hit, sending out packet to Port. %d" % self.mac_to_port[packet.dst])
      self.resend_packet(packet_in, self.mac_to_port[packet.dst])

      log.debug("Installing flow ...")
      log.debug("MATCH: In Port :  %s" % packet_in.in_port)
      log.debug("MATCH: Source MAC :  %s" % packet.src)
      log.debug("MATCH: Destination MAC :  %s" % packet.dst)
      log.debug("ACTION: Out Port :  %s" % self.mac_to_port[packet.dst])

      msg = of.ofp_flow_mod()
      msg.match.in_port = self.mac_to_port[packet.src]
      msg.match.dl_src = packet.src
      msg.match.dl_dst = packet.dst
      msg.actions.append(of.ofp_action_output(port=self.mac_to_port[packet.dst]))
      msg.idle_timeout = 60
      msg.hard_timeout = 600
      msg.buffer_id = packet_in.buffer_id
      self.connection.send(msg)

    else:
      # Flood the packet out everything but the input port
      self.resend_packet(packet_in, of.OFPP_ALL)

  def _handle_PacketIn (self, event):
    """
    Handles packet in messages from the switch.
    """

    packet = event.parsed # This is the parsed packet data.
    if not packet.parsed:
      log.warning("Ignoring incomplete packet")
      return

    packet_in = event.ofp # The actual ofp_packet_in message.

    # Comment out the following line and uncomment the one after
    # when starting the exercise.
    # self.act_like_hub(packet, packet_in)
    self.act_like_switch(packet, packet_in)



def launch ():
  """
  Starts the component
  """
  def start_switch (event):
    log.debug("Controlling %s" % (event.connection,))
    Tutorial(event.connection)
  core.openflow.addListenerByName("ConnectionUp", start_switch)

3.Results

3.1 Act like hub

使用tcpdump对接口的数据包进行筛选抓取

Benchmark Hub Controller w/iperf

3.2 Act like switch

使用tcpdump对接口的数据包进行筛选抓取

Benchmark Hub Controller w/iperf

使用编程实现的Switch，其带宽为8Gbit/s，远大于由hub实现的18Mbit/s。
实验证明，交换机的带宽远大于集线器。