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实验3:OpenFlow协议分析实践

时间:2022-10-06 00:11:35浏览次数:51  
标签:OFPT struct OpenFlow 实践 header ofp 交换机 实验 message

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

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。
主机 IP地址
h1 192.168.0.101/24
h2 192.168.0.102/24
h3 192.168.0.103/24
h4 192.168.0.104/24

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
  1. 控制器6633端口(我最高能支持OpenFlow 1.0) ----> 交换机35762端口

  1. 交换机35762端口(我最高能支持OpenFlow 1.3) ----> 控制器6633端口

于是双方建立连接,并使用 OpenFlow 1.0

  • Features Request
    控制器6633端口(我需要你的特征信息)----> 交换机35762端口

  • 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35762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35762端口(这是我的特征信息,请查收)----> 控制器6633端口

  • Packet_in
    交换机35762端口(有数据进来,请指示) ----> 控制器6633端口

  • Flow_mod(控制器收到 Packet-in 消息时的响应方式之一)
    控制器收到 Packet‐in 消息后,可以发送 Flow‐Mod 消息向交换机下发一个流表项
    控制器通过6633端口向交换机35762端口、交换机44214端口下发流表项,指导数据的转发处理

  • Packet_out
    控制器收到 Packet‐in 消息后,控制器不会下发流表,而是直接告诉交换机该如何做
    控制器6633端口向交换机35762端口发送数据,并告知交换机输出到65531端口

  • 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?
  SDN交换机和控制器在建立TCP连接的基础上进行通信

(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. OpenFlow主要消息类型
点击查看代码
enum ofp_type {
    /* Immutable messages. */
    OFPT_HELLO,               /* Symmetric message */
    OFPT_ERROR,               /* Symmetric message */
    OFPT_ECHO_REQUEST,        /* Symmetric message */
    OFPT_ECHO_REPLY,          /* Symmetric message */
    OFPT_VENDOR,              /* Symmetric message */

    /* Switch configuration messages. */
    OFPT_FEATURES_REQUEST,    /* Controller/switch message */
    OFPT_FEATURES_REPLY,      /* Controller/switch message */
    OFPT_GET_CONFIG_REQUEST,  /* Controller/switch message */
    OFPT_GET_CONFIG_REPLY,    /* Controller/switch message */
    OFPT_SET_CONFIG,          /* Controller/switch message */

    /* Asynchronous messages. */
    OFPT_PACKET_IN,           /* Async message */
    OFPT_FLOW_REMOVED,        /* Async message */
    OFPT_PORT_STATUS,         /* Async message */

    /* Controller command messages. */
    OFPT_PACKET_OUT,          /* Controller/switch message */
    OFPT_FLOW_MOD,            /* Controller/switch message */
    OFPT_PORT_MOD,            /* Controller/switch message */

    /* Statistics messages. */
    OFPT_STATS_REQUEST,       /* Controller/switch message */
    OFPT_STATS_REPLY,         /* Controller/switch message */

    /* Barrier messages. */
    OFPT_BARRIER_REQUEST,     /* Controller/switch message */
    OFPT_BARRIER_REPLY,       /* Controller/switch message */

    /* Queue Configuration messages. */
    OFPT_QUEUE_GET_CONFIG_REQUEST,  /* Controller/switch message */
    OFPT_QUEUE_GET_CONFIG_REPLY     /* Controller/switch message */

};
2. HELLO
点击查看代码
/* 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. */
};
OFP_ASSERT(sizeof(struct ofp_header) == 8);

/* OFPT_HELLO.  This message has an empty body, but implementations must
 * ignore any data included in the body, to allow for future extensions. */
struct ofp_hello {
    struct ofp_header header;
};

3. Features Request
点击查看代码
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. */
};

4. Set Config
点击查看代码
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. */
};

5. port_status

6. Features Reply
点击查看代码
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. */
};

7. Packet_in
点击查看代码
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. */
};

8. Flow_mod
点击查看代码
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. */
};

9. Packet_out
点击查看代码
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.) */
};

四、个人总结

    本次实验主要是学习通过wireshark对建立起来的拓扑进行抓包操作,分析数据包学习了OpenFlow协议下控制器和交换机的交互过程。
    通过OpenFlow源码查看OpenFlow主要消息类型对应的数据结构定义。

    1. 无法抓包OFPT_HELLO
    应该先打开wireshark再运行拓扑。
    2. 无法找到Flow_mod
    在mininet里pingall之后才会被wireshark工具捕捉到。

标签:OFPT,struct,OpenFlow,实践,header,ofp,交换机,实验,message
From: https://www.cnblogs.com/fq1242476759/p/16756842.html

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