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

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。
   
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。
   HELLO(6633->48584)最高支持openflow1.0
   
   HELLO(48584->6633)最高支持openflow1.4 则最后使用openflow1.0
   
   Features_Request
   
   Set_Config
   
   Port_Status
   
   Features_Reply
   
   Packet_in
   
   Packet_out
   
   Flow_mod
   
   OpenFlow协议中交换机与控制器的消息交互过程：
   
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？
   通过抓包信息可以看出，交换机与控制区建立通信时使用的是TCP协议。

（二）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_hello { struct ofp_header header; }; 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
   与HELLO一致

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
   `/* 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
   /* 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.) */ };

三、心得体会

这次实验只要按照说明就可以顺利的做下来，主要是让我们明白建立通信的过程，刚开始抓取hello包时，用过滤流只能抓取到一个端口向另一个端口的hello抓取不到返回的，刚开始可以不适用过滤流，抓取完hello后再使用去查看其他包。