一、实验目的

1.能够运用 wireshark 对 OpenFlow 协议数据交互过程进行抓包；

2.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

三、实验要求

（一）基本要求

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包。

拓扑代码：

#!/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')
    s1 = net.addSwitch('s1', cls=OVSKernelSwitch)
    s2 = net.addSwitch('s2', cls=OVSKernelSwitch)

    info( '*** Add hosts\n')
    h1 = net.addHost('h1', cls=Host, ip='192.168.0.101/24', defaultRoute=None)
    h2 = net.addHost('h2', cls=Host, ip='192.168.0.102/24', defaultRoute=None)
    h3 = net.addHost('h3', cls=Host, ip='192.168.0.103/24', defaultRoute=None)
    h4 = net.addHost('h4', cls=Host, ip='192.168.0.104/24', 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('s1').start([c0])
    net.get('s2').start([c0])

    info( '*** Post configure switches and hosts\n')

    CLI(net)
    net.stop()

if __name__ == '__main__':
    setLogLevel( 'info' )
    myNetwork()

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。
wireshark抓包结果
（1）OFPT_HELLO
控制器6633端口（我最高能支持OpenFlow 1.0） ---> 交换机45964端口

交换机45964端口（我最高能支持OpenFlow 1.5） ---> 控制器6633端口

（2）Features_Request
控制器6633端口（我需要你的特征信息） ---> 交换机45964端口

（3）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45964端口

（4）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。

（5）Features_Reply
交换机45964端口（这是我的特征信息，请查收） ---> 控制器6633端口

（6）Packet_in
交换机45964端口（有数据包进来，请指示）--- 控制器6633端口

（7）Packet_out
控制器6633端口--->交换机45964端口（请按照我给你的action进行处理）

(8)Flow_mod
分析抓取的flow_mod数据包，控制器通过6633端口向交换机45964端口、交换机45980端口下发流表项，指导数据的转发处理

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？
答：使用TCP协议。

（二）进阶要求
OpenFlow的数据包头具有通用字段，相关数据结构定义如下：

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. */
};
OFP_ASSERT(sizeof(struct ofp_header) == 8);

1.HELLO

/* Header on all OpenFlow packets. */
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. */
};
OFP_ASSERT(sizeof(struct ofp_header) == 8);

/* OFPT_HELLO.  This message has an empty body, but implementations must
 * ignore any data included in the body, to allow for future extensions. */
struct ofp_hello {
    struct ofp_header header;
};

2.Features Request

/* Description of a physical port */
struct ofp_phy_port {
    uint16_t port_no;
    uint8_t hw_addr[OFP_ETH_ALEN];
    char name[OFP_MAX_PORT_NAME_LEN]; /* Null-terminated */

    uint32_t config;        /* Bitmap of OFPPC_* flags. */
    uint32_t state;         /* Bitmap of OFPPS_* flags. */

    /* Bitmaps of OFPPF_* that describe features.  All bits zeroed if
     * unsupported or unavailable. */
    uint32_t curr;          /* Current features. */
    uint32_t advertised;    /* Features being advertised by the port. */
    uint32_t supported;     /* Features supported by the port. */
    uint32_t peer;          /* Features advertised by peer. */
};
OFP_ASSERT(sizeof(struct ofp_phy_port) == 48);

/* 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. */
};
OFP_ASSERT(sizeof(struct ofp_switch_features) == 32);

3.Set Config

/* Switch configuration. */
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. */
};
OFP_ASSERT(sizeof(struct ofp_switch_config) == 12);

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;
};
OFP_ASSERT(sizeof(struct ofp_port_status) == 64);

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. */
};
OFP_ASSERT(sizeof(struct ofp_switch_features) == 32);

6.Packet_in

/* 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. */
};

/* 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. */
};
OFP_ASSERT(sizeof(struct ofp_packet_in) == 20);

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.) */
};
OFP_ASSERT(sizeof(struct ofp_packet_out) == 16);

8.Flow_mod

/* Modify behavior of the physical port */
struct ofp_port_mod {
    struct ofp_header header;
    uint16_t port_no;
    uint8_t hw_addr[OFP_ETH_ALEN]; /* The hardware address is not
                                      configurable.  This is used to
                                      sanity-check the request, so it must
                                      be the same as returned in an
                                      ofp_phy_port struct. */

    uint32_t config;        /* Bitmap of OFPPC_* flags. */
    uint32_t mask;          /* Bitmap of OFPPC_* flags to be changed. */

    uint32_t advertise;     /* Bitmap of "ofp_port_features"s.  Zero all
                               bits to prevent any action taking place. */
    uint8_t pad[4];         /* Pad to 64-bits. */
};
OFP_ASSERT(sizeof(struct ofp_port_mod) == 32);

三.实验总结
本次实验的难度不大，但在实验过程中还是遇到了一些小问题
1.没有出现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。在抓包中没有出现FLOW_MOD是由于需要在pingall后才有Flow_Mod数据包
2.wireshark抓包要在构建拓扑前
3.在第一次抓包时没有出现Port_Status，但在重新进行抓包后又出现了
总之，在实验过程中要做到细心，跟着PPT做应该没有太大的问题。