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.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

1.下载虚拟机软件Oracle VisualBox；
2.在虚拟机中安装Ubuntu 20.04 Desktop amd64，并完整安装Mininet；

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。

主机	IP地址
h1	192.168.0.101/24
h2	192.168.0.102/24
h3	192.168.0.103/24
h4	192.168.0.104/24

2.保存拓扑文件

3.运行wireshark，选择any模式进行抓包，开启另一个终端，命令行运行031902344.py文件，运行pingall

4.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

4.1.OFPT_HELLO控制器6633端口 ---> 交换机36052端口,从控制器到交换机

4.2.OFPT_HELLO 源端口36052-> 目的端口6633，从交换机到控制器，此处协议为openflow1.5

控制器与交换机建立连接，并使用OpenFlow 1.0

4.3.OFPT_FEATURES_REQUEST 源端口6633 -> 目的端口36052，从控制器到交换机

控制器请求交换器的特征信息

4.4.OFPT_SET_CONFIG 源端口6633 -> 目的端口36052，从控制器到交换机

控制器要求交换机按照所给出的信息进行配置

4.5.OFPT_PORT_STATUS 源端口36052-> 目的端口6633，从交换机到控制器

当交换机端口发生变化时，交换机告知控制器相应的端口状态

4.6.OFPT_FEATURES_REPLY 源端口36052-> 目的端口6633，从交换机到控制器

交换机告知控制器它的特征信息
4.7.OFPT_PACKET_IN 源端口36052-> 目的端口6633，从交换机到控制器

交换机告知控制器有数据包进来，请求控制器指示
4.8.OFPT_PACKET_OUT 源端口6633 -> 目的端口36052，从控制器到交换机

控制器要求交换机按照所给出的action进行处理
4.9.OFPT_FLOW_MOD 源端口6633 -> 目的端口36052，从控制器到交换机

控制器对交换机进行流表的添加、删除、变更等操作

5.交换机与控制器建立通信时是使用TCP协议还是UDP协议？
如图所示为TCP协议

（二）进阶要求

将抓包结果对照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. */
};

2.FEATURES_REQUEST

代码同上

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. */
};

4.PORT_STATUS

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

/* 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. */
};
/* 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

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

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. */
};

实验总结

1.本次实验遇到的问题：
本次实验难度适中，总体实验过程流畅，没有很大的问题。
2.实验心得：
通过本次实验，我们学会了运用 wireshark 对 OpenFlow 协议数据交互过程进行抓包，了解如何借助包解析工具，分析与解释 OpenFlow协议的数据包交互过程与机制，对wireshark的使用更加熟练。在本次实验中，我第一次抓包之后有几个数据没有记录，然后进行了第二次抓包，发现端口号有变化。为了让实验结果更加具有可读性，只能把数据再次全部截图。这提醒我记录数据要完整有连贯性，少记录一个数据可能整组数据就没有用了。本次实践进一次锻炼了我们的能力，相信这对我们未来的学习将会有很大的帮助。