实验3：OpenFlow协议分析实践

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。

控制器6633端口（我最高能支持OpenFlow 1.0） ---> 交换机58076端口

交换机58076端口（我最高能支持OpenFlow 1.3） ---> 控制器6633端口

控制器6633端口（我需要你的特征信息） ---> 交换机58076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58076端口

交换机58076端口（这是我的特征信息，请查收） ---> 控制器6633端口

• 有两种情况：
  • 交换机查找流表，发现没有匹配条目时
  • 有匹配条目但是对应的action是OUTPUT=CONTROLLER时
  • 交换机58076端口（有数据包进来，请指示）--- 控制器6633端口
    

分析抓取的flow_mod数据包，控制器通过6633端口向交换机58076端口、交换机54326端口下发流表项，指导数据的转发处理

控制器6633端口（请按照我给你的action进行处理） ---> 交换机35534端口

交互图

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. */
};

2.Features Request与hello代码段一致

3.OFPT_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.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. */
};

5.PACKET_IN

enum ofp_packet_in_reason {
    OFPR_NO_MATCH,          /* No matching flow. */
    OFPR_ACTION             /* Action explicitly output to controller. */
};
/* 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. */
};

6.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.) */
};

7.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. */
};

个人总结

关于难度

• 本次实验难度简单。基本以阅读为主，没有什么操作，属于认知性实验。通过这次实验了解并掌握了OpenFlow通讯过程中数据包的流动过程，了解了Openflow通讯过程中都存在哪些包，及其作用。

实验中遇到的问题：

• 开wireshark后创建拓扑，过滤Openflow数据包，并没有发现Flow_Mod数据包，通过了解这个包是指导数据的转发处理，通过命令行pingall就出现了这个包
• 问题2：开始在过滤后发现找不到58076给6633端口的hello报文 解决方案：取消过滤后找到了，我认为是以为他是open flow vesion 1.5导致的，使得我在openflow_v1找不到

实验收获：

• 这次实验学会用过滤器输入“OpenFlow_v1和Openflow_v6”等进行数据包过滤，运用 wireshark 对 OpenFlow 协议数据交互过程进行抓包；
• 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，将抓包结果对照OpenFlow源码，了解到OpenFlow主要消息类型对应的数据结构定义。