实验3：OpenFlow协议分析实践

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 Desktop amd64

三、实验要求

（一）基本要求

• Hello
  控制器6633端口（我最高能支持OpenFlow 1.0） ---> 交换机45476端口
  

交换机45476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45476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45476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45476端口（这是我的特征信息，请查收） ---> 控制器6633端口
  

• Packet_in
  有两种情况： (1) 交换机查找流表，发现没有匹配条目时;(2)有匹配条目但是对应的action是OUTPUT=CONTROLLER时
  交换机45476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（请按照我给你的action进行处理） ---> 交换机45476端口
  

• Flow_mod
  分析抓取的flow_mod数据包，控制器通过6633端口向交换机45476端口、交换机45488端口
  下发流表项，指导数据的转发处理
  
  

• 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
  

• 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？

是TCP协议，该信息可由报文信息中得到：

（二）进阶要求

• Hello
  

//OpenFlow的数据包头具有通用字段
struct ofp_header {
    uint8_t version;    /* OFP_VERSION. 版本号*/
    uint8_t type;       /* One of the OFPT_ constants.消息类型 */
    uint16_t length;    /* Length including this ofp_header.长度 */
    uint32_t xid;       /* Transaction id associated with this packet.
                           Replies use the same id as was in the request
                           to facilitate pairing.ID */
};

struct ofp_hello {
    struct ofp_header header;
};

• Features Request
  

/* Header on all OpenFlow packets. */
//OpenFlow的数据包头具有通用字段
struct ofp_header {
    uint8_t version;    /* OFP_VERSION. 版本号*/
    uint8_t type;       /* One of the OFPT_ constants.消息类型 */
    uint16_t length;    /* Length including this ofp_header.长度 */
    uint32_t xid;       /* Transaction id associated with this packet.
                           Replies use the same id as was in the request
                           to facilitate pairing.ID */
};

• Set Config
  

/* Switch configuration. */
struct ofp_switch_config {
    struct ofp_header header;    //通用字段
    uint16_t flags;             /* OFPC_* flags.交换机如何处理IP分片数据包 */
    uint16_t miss_send_len;     /* Max bytes of new flow that datapath should send to the controller. 交换机无法处理的到达的数据包时，将数据包发给控制器的最大字节数*/
};

• Port_Status
  

/* A physical port has changed in the datapath */
//当交换机端口发生变化时，告知控制器相应的端口状态。
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;
};

• 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.唯一标识符 */

    uint32_t n_buffers;     /* Max packets buffered at once. 交换机缓冲区可以
缓存的最大数据包个数*/

    uint8_t n_tables;       /* Number of tables supported by datapath.流表数量 */
    uint8_t pad[3];         /* Align to 64-bits.可以理解为填充值 */

    /* Features. */
    uint32_t capabilities;  /* Bitmap of support "ofp_capabilities".支持的特殊功能 */
    uint32_t actions;       /* Bitmap of supported "ofp_action_type"s.支持的动作 */

    /* Port info.*/
    struct ofp_phy_port ports[0];  /* Port definitions.  The number of ports
                                      is inferred from the length field in
                                      the header.物理端口描述列表 */
};

• Packet_in
  

//两种情况：1.交换机查找流表，发现没有匹配条目时
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,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. */
};

• 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.) */
};

• 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. */
};

四、个人总结

实验遇到的困难及解决方法

在整个实验过程当中，主要遇到的问题在刚开始建立拓扑时设置ip地址时太粗心了出错，后面经过检查发现问题及时改正；还有就是在抓包时没有抓到关于openflow协议的数据包，后面发现是自己忘记先点any了，经过舍友的指导后进行订正，后面顺利抓到相关数据包，且需要注意的是，选择any选项时一定要sudo。

个人感想

整个实验其实还是比较简单的，但是在越简单的实验当中其实细节往往就决定了成功的快慢，在这个实验当中是深有体会的，且在遇到困难又想不出问题所在时一定要大胆寻求帮助，这会使你豁然开朗。在这个实验当中也有学到怎么解锁文件等知识，也体会到了知识只有在遇到问题拿去实践时才成为自己所掌握的一部分。