实验三：OpenFlow协议分析实践

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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

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。
   

• 修改主机IP地址和 控制器IP：
  
  

2. 保存拓扑文件
   

3. 首先打开一个终端输入sudo wireshark打开wires hark，选择any进行抓包，然后打开另一个终端打开保存的拓扑文件。
   

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

• OFPT_HELLO控制器6633端口 ---> 交换机38216端口,从控制器到交换机
  

• OFTP_HELLO 交换机38216端口---> 控制器6633端口
  
  双方建立连接，并使用OPenflow 1.0

• OFTP_FEATRUES_REQUEST控制器6633端口 ---> 交换机38216端口，从控制器到交换机。控制器请求交换器的特征信息
  

• OFTP_SET_CONFIG控制器6633端口 ---> 交换机38216端口。控制器要求交换机按照所给出的信息进行配置
  

• OFTP_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。
  

• OFTP_FEATURES_REPLY交换机38216端口---> 控制器6633端口。交换机告知控制器它的特征信息
  

• OFTP_PACKET_IN交换机38216端口（有数据包进来，请指示）--- 控制器6633端口
  

• OFTP_FLOW_MOD分析抓取的flow_mod数据包，控制器通过6633端口向交换机38216端口、交换机38216端下发流表项，指导数据的转发处理
  

• OFTP_PACKET_OUT控制器6633端口 ---> 交换机38216端口
  

• 回答：交换机与控制器建立通信时是使用TCP协议还是UDP协议？
  
  采用的是TCP协议

• 流程图
  

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
   

/* 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. */
};

2. FEATURES_REQUEST
   
   与HELLO的代码段一致

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_REPLAY
   

/* 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
   

/* 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.) */
};

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

• 遇到的问题：在实验过程遇到的问题是，在实验过程中没抓到OPEN＿FLOW的包，连续试了几次都没有这个包，后来在网上查阅了相关的资料，在运行完成保存的拓扑文件之后还需要进行一次ｐｉｎｇ操作，这样wireshark　才能抓到ｏｐｅｎｆｌｏｗ的包。
• 实验感想：这次实验难度适中，在整个过程中还算是比较流畅，但是我在实验的过程中连续抓了好几次包，实验过程截图并不是在一个包里面截图的，导致在实验报告里面出现了许多不同的端口号，实验报告是以我的第一包为准即端口号38216；我的实验是分两次做的，进阶要求部分吸取了第一次实验的教训，一次操作就完成了，截图也是在抓到的同一个包里面截图的即端口号38832；最后在ｏｐｅｎｌｏｗ的源码里面找到相应部分的源码花费了较多的时间，整个实验做下来还算流畅。

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