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

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

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

1.IP配置

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.

1).OFPT_HELLO 源端口6633 -> 目的端口38904，从控制器到交换机,此处协议为openflow1.0

2).源端口38904 -> 目的端口6633的，即交换机到控制器的另一个包，此处协议为openflow1.5

3).OFPT_FEATURES_REQUEST 源端口6633 -> 目的端口38904，从控制器到交换机. (控制器请求交换器的特征信息)

4).OFPT_SET_CONFIG 源端口6633 -> 目的端口38904，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)

5).OFPT_PORT_STATUS 源端口38904 -> 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)

6).OFPT_FEATURES_REPLY 源端口38904 -> 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)

7).OFPT_PACKET_IN 源端口38904 -> 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)

8).OFPT_PACKET_OUT 源端口6633 -> 目的端口38904，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)

9).OFPT_FLOW_MOD 源端口6633 -> 目的端口38904，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)

3.画出相关交互图。

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？
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。相关数据结构可在openflow安装目录openflow/include/openflow当中的openflow.h头文件中查询到
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.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. */
};

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

/* 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

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. */
};
/* 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. */
};

6.PACKET_IN (有两种情况)
(1).交换机查找流表，发现没有匹配条目

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

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

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. */
};
struct ofp_action_header {
  uint16_t type;                  /* One of OFPAT_*. */
  uint16_t len;                   /* Length of action, including this
                                     header.  This is the length of action,
                                     including any padding to make it
                                     64-bit aligned. */
  uint8_t pad[4];
};

四.实验总结

1.实验难度：实验难度适中，步骤较少，比较好理解。
2.实验过程遇到的困难及解决办法：在开始抓包的时候不知道使用过滤工具，导致重要信息不好发现，
通过选择过滤规则openflow_v1，可以发现只有openflow1.0和openflow1.5的数据包，能够快速的找到信息所在位置。
3.实验心得：本次实验较为简单，最主要是观察OpenFlow协议的数据包交互过程与机制，了解控制器和交换机之间的信息交换，
了解结构体中的信息，分析数据包，让我对交换机与控制器的消息交互过程更加熟悉。

标签：控制器,struct,OpenFlow,端口,实践,header,ofp,交换机,实验
来源： https://www.cnblogs.com/eiheihei233/p/15346059.html