其他分享
首页 > 其他分享> > 实验3：OpenFlow协议分析实践

实验3：OpenFlow协议分析实践

作者：互联网

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

  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。
    img
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

  1. 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。

    由于题述拓扑中存在两个交换机，这里只以其中一个交换机与控制器的交互作为说明

    • Hello

      交换机和控制器互相发送Hello报文，控制器默认使用OpenFlow1.0版本，交换机我们先前设置其支持OpenFlow1.0和1.3，这里交换机使用所能支持的最高版本OpenFlow1.3进行通信。最后按照规定两者以较低版本1.0进行通信

      控制器6633端口（我最高能支持OpenFlow 1.0） ---> 交换机33616端口

      image-20210923165106663

      交换机33616端口（我最高能支持OpenFlow 1.3）---> 控制器6633端口

      image-20210923165444509

    • Features Request / Set Config

      控制器向交换机发送FEATURES_REQUEST询问交换机信息

      控制器向交换机发送SET_CONFIG配置相关指标

      控制器6633端口（我需要你的特征信息） ---> 交换机33616端口

      image-20210923170913286

      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33616端口

      image-20210923170951124

    • 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

      image-20210923171423525

    • Features Reply

      交换机收到Features Request之后随即发送Features Reply，将自己的信息发送至控制器

      交换机33616端口（这是我的特征信息，请查收）---> 控制器6633端口

      image-20210923171811570

    • Packet_in

      出现Packet_in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33616端口（有数据包进来，请指示）--- 控制器6633端口

      image-20210923172148834

    • Packet_out

      控制器6633端口（请按照我给你的action进行处理） ---> 交换机33616端口

      image-20210923172456141

    • Flow_mod

      在该过程中我并未抓取到该类型的数据包

    • 相关交互图

      image-20210923192527064

      由于Features Request / Set Config和Packet_out / Flow_mod没有明显的先后关系所以放在一起

  2. 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？

    使用了TCP协议，抓包截图与topo.py源码中均能体现

    image-20210922221030644

    image-20210923165416855

（二）进阶要求

  1. 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。

    • Hello

      image-20210923194747012

      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. */
};
struct ofp_hello {
    struct ofp_header header;
};

    • Features Request

      image-20210923170913286

      可以发现这一个消息类型的格式与Hello一致，含有一个头部ofp_header

    • Set Config

      image-20210923170951124

      /* 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. */
};

      以上可以看出这个消息类型用于控制器向交换机发送配置信息

    • Port_Status

      image-20210923171423525

      /* 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;
};

    • Features Reply

      image-20210923195827138

      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. */
};

    • Packet_in

      image-20210923200116321

      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. */

      除以上与这种情况外，还有Packet_in数据报还有一种：

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

    • Packet_out

      image-20210923200417915

      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

      由于未找到这种数据包这里只有对应的源码

      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. */
};
struct ofp_action_header {
    uint16_t type;                  /* One of OFPAT_*. */
    uint16_t len;                   /* Length of action, including this
                                       header.  This is the length of action,
                                       including any padding to make it
                                       64-bit aligned. */
    uint8_t pad[4];
};

四、个人总结

标签：控制器,struct,uint16,OpenFlow,实践,header,ofp,交换机,实验
来源： https://www.cnblogs.com/beyondzones/p/15327257.html