sdn第六次实践作业
(一)
运行截图：
tcpdump验证过程：
（h2和h3都收到了h1的数据包）
分析：L2 Switch模块和POX的hub无太大区别，都是使用OFPP_FLOOD标记让数据包向所有端口发送,
分析代码：Hub模块有被动和主动两个方式，被动是处理每个数据包然后让他们泛洪，主动是给交换机下发流表，告诉每个交换机去泛洪。L2 Switch是直接构造一个数据去泛洪。
(二)进阶
simple_switch13的源代码与注释
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):
OFP_VERSIONS = [ofproto_v1_3.OFP_VERSION] #标注版本号为1.3
def __init__(self, *args, **kwargs): # 初始化类
super(SimpleSwitch13, self).__init__(*args, **kwargs)
self.mac_to_port = {} # 初始化mac_to_port数组
@set_ev_cls(ofp_event.EventOFPSwitchFeatures, CONFIG_DISPATCHER)
def switch_features_handler(self, ev): # 安装无目标的流表条目
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)
def add_flow(self, datapath, priority, match, actions, buffer_id=None): # 增加流表
ofproto = datapath.ofproto
parser = datapath.ofproto_parser
inst = [parser.OFPInstructionActions(ofproto.OFPIT_APPLY_ACTIONS,
actions)]
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)
datapath.send_msg(mod)
# 构建一个流量调制信息并发送
@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)
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]
if eth.ethertype == ether_types.ETH_TYPE_LLDP:
# ignore lldp packet
return
dst = eth.dst
src = eth.src # 用packet library分析收到的数据包
dpid = format(datapath.id, "d").zfill(16)# 获得Datapath ID以便于识别OpenFlow交换机
self.mac_to_port.setdefault(dpid, {})
self.logger.info("packet in %s %s %s %s", dpid, src, dst, in_port)
# learn a mac address to avoid FLOOD next time.
# 记录mac地址以避免下次的消息范洪
self.mac_to_port[dpid][src] = in_port
if dst in self.mac_to_port[dpid]: # 如果目标Mac地址已经被学习了，决定哪个从哪个端口发送数据包。否则范洪
out_port = self.mac_to_port[dpid][dst]
else:
out_port = ofproto.OFPP_FLOOD
actions = [parser.OFPActionOutput(out_port)] #构造action表
# install a flow to avoid packet_in next time
# 安装流表以避免下次pactet_in
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
# 构造一个pack_out消息然后发送
out = parser.OFPPacketOut(datapath=datapath, buffer_id=msg.buffer_id,
in_port=in_port, actions=actions, data=data)
datapath.send_msg(out)
a) 代码当中的mac_to_port的作用是什么？
答：记录mac地址以避免下次的消息Flood
b) simple_switch和simple_switch_13在dpid的输出上有何不同？
答：simple_switch_13对dpid进行了格式化，并填充为16位数字
c) 相比simple_switch，simple_switch_13增加的switch_feature_handler实现了什么功能？
答：安装无目标的流表条目
d) simple_switch_13是如何实现流规则下发的？
答：构造一个flow_mod消息并发送
e) switch_features_handler和_packet_in_handler两个事件在发送流规则的优先级上有何不同
答：switch_features_handler发送的priority=0，_packet_in_handler发送的流表的priority设置为1
心得体会
RYU的安装代码参考：
git clone https://github.com/faucetsdn/ryu.git
cd ryu
sudo pip3 install -r tools/pip-requires -i https://pypi.tuna.tsinghua.edu.cn/simple
sudo python3 setup.py install
L2Switch源码
from ryu.base import app_manager
from ryu.controller import ofp_event
from ryu.controller.handler import MAIN_DISPATCHER
from ryu.controller.handler import set_ev_cls
from ryu.ofproto import ofproto_v1_0
class L2Switch(app_manager.RyuApp):
OFP_VERSIONS = [ofproto_v1_0.OFP_VERSION]
def __init__(self, *args, **kwargs):
super(L2Switch, self).__init__(*args, **kwargs)
@set_ev_cls(ofp_event.EventOFPPacketIn, MAIN_DISPATCHER)
def packet_in_handler(self, ev):
msg = ev.msg
dp = msg.datapath
ofp = dp.ofproto
ofp_parser = dp.ofproto_parser
actions = [ofp_parser.OFPActionOutput(ofp.OFPP_FLOOD)]
data = None
if msg.buffer_id == ofp.OFP_NO_BUFFER:
data = msg.data
out = ofp_parser.OFPPacketOut(
datapath=dp, buffer_id=msg.buffer_id, in_port=msg.in_port,
actions=actions, data = data)
dp.send_msg(out)
遇到困难：可视化拓扑图光秃秃的只有一个交换机
原因：本来就只能显示交换机。和ODL不一样。尴尬
L2Switch的代码似乎为了教学而写的简单。在文档下面也写了觉得这个L2Switch太蠢？可以自己写。。
进阶心得：反正就是找资料。不然还要理解源码还要理解ryu的各个组件有什么作用。
