实验3:OpenFlow协议分析实践

实验3:OpenFlow协议分析实践

一、拓扑文件

二、wireshark抓包分析

(1)OFPT_HELLO

控制器6633端口(最高支持OpenFlow 1.0) ---> 交换机58074端口

交换机58074端口(最高支持OpenFlow 1.3)--->控制器6633端口

(2)OFPT_Features_Request

控制器6633端口(我需要你的特征信息) ---> 交换机58074端口

(3)OFPT_Set_Config

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

(4)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。

(5)Features_Reply

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

(6)Packet_in

交换机58074端口(有数据包进来,请指示)--- 控制器6633端口

7)Packet_out

控制器6633端口--->交换机58074端口(请按照我给你的action进行处理)

(8)open_flow_mod

2. 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。

img

3.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?

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。

/* 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. */
};

OpenFlow数据包头的通用字段,分别是版本号,消息类型,长度,ID

·HELLO

struct ofp_hello {
    struct ofp_header header;
};

HELLO报文用于协商协议,双方发送本方支持的最高版本的协议。最终会使用双方都支持的最低版本协议建立连接。type处会被置为OFPT_HELLO

·FEATURES REQUEST

struct ofp_hello {
    struct ofp_header header;
};

结构与HELLO一致。

·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. */
};

·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;
};

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

/* 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. */
};

·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. */
};

·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.) */
};

·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. */
};

(三)个人总结

这次实验较前几次实验,难度确实减小了,但是实验报告要求的一些抓包会比较繁琐,从而考验耐心和细心。特别要注意的是要先开启wireshark再建立拓扑,否则会导致部分包抓取不到;除此以外,在建立拓扑结构的时候,记得要把preferences里面的IP Base改成192.168.0.0/24,不然同样也会出错。这次实验遇到的难题大致就上述所说,由于这次遇到的困难并不算很困难,所以在我就没有查阅资料和问同学,在自己的尝试下解决了这些问题。

posted @ 2022-09-27 22:56  VJJJJJJ  阅读(44)  评论(0编辑  收藏  举报