实验6：开源控制器实践——RYU
实验6：开源控制器实践——RYU
安装截图
拓扑可视化
tcpdump查看
h1 ping h2
h1 ping h3
可以看到均为洪泛转发
查看控制器流表，如下图：
看到没有流表，而使用pox的hub模块则会看到流表，如下图：
所以可以看到二者都是洪泛转发，但是不同之处在于POX是直接向交换机下发流表，而Ryu是在每个 Packet In 事件之后，向交换机下发动作。
进阶要求
simple_switch_13.py代码注释
# Copyright (C) 2011 Nippon Telegraph and Telephone Corporation.
#
# 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.
# 引入包
from ryu.base import app_manager
from ryu.controller import ofp_event
from ryu.controller.handler import CONFIG_DISPATCHER, MAIN_DISPATCHER
from ryu.controller.handler import set_ev_cls
from ryu.ofproto import ofproto_v1_3
from ryu.lib.packet import packet
from ryu.lib.packet import ethernet
from ryu.lib.packet import ether_types
class SimpleSwitch13(app_manager.RyuApp):
# 定义openflow版本
OFP_VERSIONS = [ofproto_v1_3.OFP_VERSION]
def __init__(self, *args, **kwargs):
super(SimpleSwitch13, self).__init__(*args, **kwargs)
# 定义保存mac地址到端口的一个映射
self.mac_to_port = {}
# 处理EventOFPSwitchFeatures事件
@set_ev_cls(ofp_event.EventOFPSwitchFeatures, CONFIG_DISPATCHER)
def switch_features_handler(self, ev):
datapath = ev.msg.datapath
ofproto = datapath.ofproto
parser = datapath.ofproto_parser
# install table-miss flow entry
#
# We specify NO BUFFER to max_len of the output action due to
# OVS bug. At this moment, if we specify a lesser number, e.g.,
# 128, OVS will send Packet-In with invalid buffer_id and
# truncated packet data. In that case, we cannot output packets
# correctly. The bug has been fixed in OVS v2.1.0.
match = parser.OFPMatch()
actions = [parser.OFPActionOutput(ofproto.OFPP_CONTROLLER,
ofproto.OFPCML_NO_BUFFER)]
self.add_flow(datapath, 0, match, actions)
# 添加流表函数
def add_flow(self, datapath, priority, match, actions, buffer_id=None):
# 获取交换机信息
ofproto = datapath.ofproto
parser = datapath.ofproto_parser
# 对action进行包装
inst = [parser.OFPInstructionActions(ofproto.OFPIT_APPLY_ACTIONS,
actions)]
# 判断是否有buffer_id，生成mod对象
if buffer_id:
mod = parser.OFPFlowMod(datapath=datapath, buffer_id=buffer_id,
priority=priority, match=match,
instructions=inst)
else:
mod = parser.OFPFlowMod(datapath=datapath, priority=priority,
match=match, instructions=inst)
# 发送mod
datapath.send_msg(mod)
# 处理 packet in 事件
@set_ev_cls(ofp_event.EventOFPPacketIn, MAIN_DISPATCHER)
def _packet_in_handler(self, ev):
# If you hit this you might want to increase
# the "miss_send_length" of your switch
if ev.msg.msg_len < ev.msg.total_len:
self.logger.debug("packet truncated: only %s of %s bytes",
ev.msg.msg_len, ev.msg.total_len)
# 获取包信息，交换机信息，协议等等
msg = ev.msg
datapath = msg.datapath
ofproto = datapath.ofproto
parser = datapath.ofproto_parser
in_port = msg.match['in_port']
pkt = packet.Packet(msg.data)
eth = pkt.get_protocols(ethernet.ethernet)[0]
# 忽略LLDP类型
if eth.ethertype == ether_types.ETH_TYPE_LLDP:
# ignore lldp packet
return
# 获取源端口，目的端口
dst = eth.dst
src = eth.src
dpid = format(datapath.id, "d").zfill(16)
self.mac_to_port.setdefault(dpid, {})
self.logger.info("packet in %s %s %s %s", dpid, src, dst, in_port)
# 学习包的源地址，和交换机上的入端口绑定
# learn a mac address to avoid FLOOD next time.
self.mac_to_port[dpid][src] = in_port
# 查看是否已经学习过该目的mac地址
if dst in self.mac_to_port[dpid]:
out_port = self.mac_to_port[dpid][dst]
# 否则进行洪泛
else:
out_port = ofproto.OFPP_FLOOD
actions = [parser.OFPActionOutput(out_port)]
# 下发流表处理后续包，不再触发 packet in 事件
# install a flow to avoid packet_in next time
if out_port != ofproto.OFPP_FLOOD:
match = parser.OFPMatch(in_port=in_port, eth_dst=dst, eth_src=src)
# verify if we have a valid buffer_id, if yes avoid to send both
# flow_mod & packet_out
if msg.buffer_id != ofproto.OFP_NO_BUFFER:
self.add_flow(datapath, 1, match, actions, msg.buffer_id)
return
else:
self.add_flow(datapath, 1, match, actions)
data = None
if msg.buffer_id == ofproto.OFP_NO_BUFFER:
data = msg.data
out = parser.OFPPacketOut(datapath=datapath, buffer_id=msg.buffer_id,
in_port=in_port, actions=actions, data=data)
# 发送流表
datapath.send_msg(out)
代码当中的mac_to_port的作用是什么？
保存mac地址到交换机端口的映射，为交换机自学习功能提供数据结构进行 mac-端口 的存储
simple_switch和simple_switch_13在dpid的输出上有何不同？
simple_switch的dpid赋值：dpid = datapath.id
simple_switch_13的dpid赋值：dpid = format(datapath.id, "d").zfill(16)
在python console进行测试，可以看到在simple_switch直接获取的id，在simple_switch_13中，会在前端加上0将其填充至16位
相比simple_switch，simple_switch_13增加的switch_feature_handler实现了什么功能？
实现交换机以特性应答消息响应特性请求，可查看文档
simple_switch_13是如何实现流规则下发的？
在接收到packetin事件后，首先获取包学习，交换机信息，以太网信息，协议信息等。如果以太网类型是LLDP类型，则不予处理。如果不是，则获取源端口目的端口，以及交换机id，先学习源地址对应的交换机的入端口，再查看是否已经学习目的mac地址，如果没有则进行洪泛转发。如果学习过该mac地址，则查看是否有buffer_id，如果有的话，则在添加流动作时加上buffer_id，向交换机发送流表。
总结
本次实验难度较难，主要在于对openflow协议的理解，以及对Ryu源码的熟悉程度。在实验过程中，遇到如下问题：
- 在用Ryu的L2Switch模块下发流表时，看到洪泛现像，但是在交换机上没有看到流表，在请教老师之后才知道，这才是Ryu与POX之间的差别
- 在分析simple_switch.py和simple_switch_13.py源码时，遇到困难，不理解函数的作用，在查看官方文档，以及搜索相关资料之后，对源码的理解相对透彻了些
这次实验相比上次难度更大，对源码分析和对openflow协议的理解有一定的要求，但是做完实验后感受到收获颇多，学习到了更多的知识。
