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

查看抓包结果

• hello
  控制器6633端口（我最高支持OpenFlow1.0）--->交换机52148端口

交换机52148端口（我最高支持OpenFlow1.3）--->控制器6633端口

• Features Request/Set Config

控制器6633端口（我需要你的特征信息） ---> 交换机52148端口

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52148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51422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54122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54122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51422端口、交换机51438端口下发流表项，指导数据的转发处理

• 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？
  tcp协议

（二）进阶要求

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. */
};

//HELLO报文中有四个参数，对应版本号、消息类型、长度及ID，ID是唯一的，回复使用相同的ID
struct ofp_hello {
    struct ofp_header header;
};
//HELLO报文中的body是空的，只有一个头部。

2. Features Request

/* 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. */
};

 //feature_request的结构和hello一样

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. */
};
//除了头部，还有端口类型，以及packet可携带的最大消息长度

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;
};
//添加、删除或修改物理端口时，需要发送Port-Status 消息来通知OpenFlow 控制器

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

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.) */
};

//包括动作列表、缓冲区ID等

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. */
};

//包括流表项标志符cookie，command代表五种操作，对应值分别为0-4，优先级等

（四）个人总结

1. 这次实验难度较小，属于验证性观察实验，按照实验指导作，基本没有什么大的问题。遇到的一些困难就是，在进行抓包时，第一次有看到openflow_v4,但是再次运行导出的Python文件时却发现没有openflow_v4,但有openflow_v6，显示的是1.5协议。就是发现第一次构造topo时可以抓取到1.3。后来发现两者都可以。
2. 通过这次实验学习到了controller通过openflow协议进行与交换机的通信过程，以及端口配置。controller和switches通信是通过TCP协议，建立起可靠传输，里面包裹openflow协议。通过和源码对照，能够直观的认识到不同类型的数据报的组成，以及各字段所代表的意义和作用。