实验3：OpenFlow协议分析实践
一、实验目的
能够运用 wireshark 对 OpenFlow 协议数据交互过程进行抓包；
能够借助包解析工具，分析与解释 OpenFlow协议的数据包交互过程与机制。
二、实验环境
Ubuntu 20.04 Desktop amd64
三、实验要求
1.搭建下图所示拓扑，完成相关 IP 配置，并实现主机与主机之间的 IP 通信。用抓包软件获取控制器与交换机之间的通信数据。
搭建拓扑结构
代码：
#!/usr/bin/env python
from mininet.net import Mininet
from mininet.node import Controller, RemoteController, OVSController
from mininet.node import CPULimitedHost, Host, Node
from mininet.node import OVSKernelSwitch, UserSwitch
from mininet.node import IVSSwitch
from mininet.cli import CLI
from mininet.log import setLogLevel, info
from mininet.link import TCLink, Intf
from subprocess import call
def myNetwork():
net = Mininet( topo=None,
build=False,
ipBase='192.168.0.0/24')
info( '*** Adding controller\n' )
c0=net.addController(name='c0',
controller=Controller,
protocol='tcp',
port=6633)
info( '*** Add switches\n')
s2 = net.addSwitch('s2', cls=OVSKernelSwitch)
s1 = net.addSwitch('s1', cls=OVSKernelSwitch)
info( '*** Add hosts\n')
h2 = net.addHost('h2', cls=Host, ip='192.168.0.102/24', defaultRoute=None)
h4 = net.addHost('h4', cls=Host, ip='192.168.0.104/24', defaultRoute=None)
h3 = net.addHost('h3', cls=Host, ip='192.168.0.103/24', defaultRoute=None)
h1 = net.addHost('h1', cls=Host, ip='192.168.0.101/24', defaultRoute=None)
info( '*** Add links\n')
net.addLink(h1, s1)
net.addLink(s1, h3)
net.addLink(s1, s2)
net.addLink(s2, h2)
net.addLink(s2, h4)
info( '*** Starting network\n')
net.build()
info( '*** Starting controllers\n')
for controller in net.controllers:
controller.start()
info( '*** Starting switches\n')
net.get('s2').start([c0])
net.get('s1').start([c0])
info( '*** Post configure switches and hosts\n')
CLI(net)
net.stop()
if __name__ == '__main__':
setLogLevel( 'info' )
myNetwork()
ping通结果
2.查看抓包结果
OFPT_HELLO:
从控制器6633端口到交换机48008端口，使用OpenFlow1.0协议：
交换机48008端口（我最高能支持OpenFlow 1.5） ---> 控制器6633端口
于是双方建立连接，并使用OpenFlow 1.0
FEATURES_REQUEST
控制器6633端口（我需要你的特征信息） ---> 交换机48008端口
SET_CONFIG
控制器6633端口（请按照我给你的flag和max bytes of packet进行配置） ---> 交换机48008端口
PORT_STATUS
当交换机端口发生变化时，告知控制器相应的端口状态
FEATURES_REPLY
交换机48008端口（这是我的特征信息，请查收） ---> 控制器6633端口
PACKET_IN
交换机48008端口（有数据包进来，请指示）--->控制器6633端口
PACKET_OUT
控制器6633端口--->交换机48008端口（请按照我给你的action进行处理）
FLOW_MOD
分析抓取的flow_mod数据包，控制器通过6633端口向交换机48008端口、交换机48008端口下发流表项，指导数据的转发处理
2.查看抓包结果，分析OpenFlow协议中交换机与控制器的消息交互过程，画出相关交互图或流程图。
3.回答问题：交换机与控制器建立通信时是使用TCP协议还是UDP协议？
由上图可知，是TCP协议
四、进阶要求
将抓包基础要求第2步的抓包结果对照OpenFlow源码，了解OpenFlow主要消息类型对应的数据结构定义。
1.HELLO
struct ofp_header
{
uint8_t version; /* OFP_VERSION. */
uint8_t type; /* One of the OFPT_ constants. */
uint16_t length; /* Length including this ofp_header. */
uint32_t xid; /* Transaction id associated with this packet.
Replies use the same id as was in the request
to facilitate pairing. */
};
struct ofp_hello
{
struct ofp_header header;
};
2.OFPT_FEATURES_REQUEST
struct ofp_header
{
uint8_t version; /* OFP_VERSION. */
uint8_t type; /* One of the OFPT_ constants. */
uint16_t length; /* Length including this ofp_header. */
uint32_t xid; /* Transaction id associated with this packet.
Replies use the same id as was in the request
to facilitate pairing. */
};
struct ofp_hello
{
struct ofp_header header;
};
3.SET_CONFIG
struct ofp_switch_config
{
struct ofp_header header;
uint16_t flags; /* OFPC_* flags. */
uint16_t miss_send_len; /* Max bytes of new flow that datapath should
send to the controller. */
};
4.PORT_STATUS
/* A physical port has changed in the datapath */
struct ofp_port_status
{
struct ofp_header header;
uint8_t reason; /* One of OFPPR_*. */
uint8_t pad[7]; /* Align to 64-bits. */
struct ofp_phy_port desc;
};
5.FEATURES_REPLY
/* Switch features. */
struct ofp_switch_features
{
struct ofp_header header;
uint64_t datapath_id; /* Datapath unique ID. The lower 48-bits are for
a MAC address, while the upper 16-bits are
implementer-defined. */
uint32_t n_buffers; /* Max packets buffered at once. */
uint8_t n_tables; /* Number of tables supported by datapath. */
uint8_t pad[3]; /* Align to 64-bits. */
/* Features. */
uint32_t capabilities; /* Bitmap of support "ofp_capabilities". */
uint32_t actions; /* Bitmap of supported "ofp_action_type"s. */
/* Port info.*/
struct ofp_phy_port ports[0]; /* Port definitions. The number of ports
is inferred from the length field in
the header. */
};
6.PACKET_IN
（1）交换机查找流表，发现没有匹配条目，但未发现这种情况。
/* Why is this packet being sent to the controller? */
enum ofp_packet_in_reason
{
OFPR_NO_MATCH, /* No matching flow. */
OFPR_ACTION /* Action explicitly output to controller. */
};
（2）有匹配条目,对应的action是OUTPUT=CONTROLLER,固定收到向控制器发送包
/* Packet received on port (datapath -> controller). */
struct ofp_packet_in
{
struct ofp_header header;
uint32_t buffer_id; /* ID assigned by datapath. */
uint16_t total_len; /* Full length of frame. */
uint16_t in_port; /* Port on which frame was received. */
uint8_t reason; /* Reason packet is being sent (one of OFPR_*) */
uint8_t pad;
uint8_t data[0]; /* Ethernet frame, halfway through 32-bit word,
so the IP header is 32-bit aligned. The
amount of data is inferred from the length
field in the header. Because of padding,
offsetof(struct ofp_packet_in, data) ==
sizeof(struct ofp_packet_in) - 2. */
};
7.PACKET_OUT
/* Send packet (controller -> datapath). */
struct ofp_packet_out
{
struct ofp_header header;
uint32_t buffer_id; /* ID assigned by datapath (-1 if none). */
uint16_t in_port; /* Packet's input port (OFPP_NONE if none). */
uint16_t actions_len; /* Size of action array in bytes. */
struct ofp_action_header actions[0]; /* Actions. */
/* uint8_t data[0]; */ /* Packet data. The length is inferred
from the length field in the header.
(Only meaningful if buffer_id == -1.) */
};
8.FLOW_MOD
/* Flow setup and teardown (controller -> datapath). */
struct ofp_flow_mod {
struct ofp_header header;
struct ofp_match match; /* Fields to match */
uint64_t cookie; /* Opaque controller-issued identifier. */
/* Flow actions. */
uint16_t command; /* One of OFPFC_*. */
uint16_t idle_timeout; /* Idle time before discarding (seconds). */
uint16_t hard_timeout; /* Max time before discarding (seconds). */
uint16_t priority; /* Priority level of flow entry. */
uint32_t buffer_id; /* Buffered packet to apply to (or -1).
Not meaningful for OFPFC_DELETE*. */
uint16_t out_port; /* For OFPFC_DELETE* commands, require
matching entries to include this as an
output port. A value of OFPP_NONE
indicates no restriction. */
uint16_t flags; /* One of OFPFF_*. */
struct ofp_action_header actions[0]; /* The action length is inferred
from the length field in the
header. */
};
个人总结
学习到的知识：
| 指令 | 作用 |
|---|---|
| OFPT_HELLO | 建立OpenFlow连接， 控制器与交换机互相发送Hello消息，Hello消息中只包含Openflow Header，双方Openflow版本需要兼容（双方所支持的最高版本） |
| FEATURES_REQUEST | 控制器向交换机发送FEATURES_REQUEST询问交换机信息 |
| SET_CONFIG | 控制器向交换机发送发送SET_CONFIG消息以发送设置信息，也可能发送GET_CONFIG请求消息以查询OpenFlow交换机的设置状态 |
| PORT_STATUS | 当交换机端口发生变化时，告知控制器相应的端口状态。 |
| FEATURES_REPLY | 交换机收到FEATURES_REQUEST之后随即发送FEATURES_REPLY，将自己的信息发送至控制器 |
| PACKET_IN | 使用Packet-In消息的目的是为了将到达OpenFlow交换机的数据包发送至OpenFlow控制器。以下2种情况即可发送Packet-In消息。不存在与流表项一致的项目时（Table-miss），OFPR_NO_MATCH；匹配的流表项中记载的行动为“发送至OpenFlow控制器”时，OFPR_ACTION |
| PACKET_OUT | Packet-Out消息是从OpenFlow控制器向OpenFlow交换机发送的消息，是包含数据包发送命令的消息”。 |
| FLOW_MOD | 控制器通过向交换机发送FLOW_MOD，来对交换机进行流表的添加、删除、变更等设置操作。 |
感想：
这次作业的难度中等，主要在于了解OpenFlow协议在交换机和控制器间的交互过程，但是在实验过程中遇到了两个问题：
- 抓包过程一点要先
sudo wireshark再运行python文件，不然很可能没抓到 - 这次的进阶要求查看源码，关键源码在openflow安装目录中的
openflow/include/openflow/openflow.h头文件里，通过不断比对源码中定义的结构体和抓到的包的报文结构，学习到openflow协议在代码上是如何体现的。
通过实验抓包以及查看openflow头文件,对OpenFlow协议中交换机与控制器的消息交互过程,以及常用的消息列表有了进一步的了解,同时对于SDN中控制与转发分离有了更深刻的了解，收益匪浅。
标签：struct,OpenFlow,实践,header,ofp,交换机,实验,net From： https://www.cnblogs.com/ljy521/p/16732823.html