实验3：OpenFlow协议分析实践

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。

|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|

  • 保存为.py文件

  • 相关IP配置

  • 运行命令sudo wireshark开启wireshark抓包工具，进入wireshark界面后点击any获取全部数据包

  • 先开启抓包再pingall

  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。
  • OFPT_HELLO
    • 控制器6633端口（我最高能支持OpenFloww1.0）--->交换机47310端口
    • 交换机47310端口（我最高能支持OpenFlow1.5）--->控制器6633端口

      于是双方建立连接，并使用OpenFlow1.0
  • OFPT_FEATURES_REQUEST
    • 控制器6633端口（我需要你的特征信息）--->交换机47310端口
  • OFPT_SET_CONFIG
    • 控制器6633端口（请按照我给你的flag和max bytes of package进行配置）--->交换机47310端口
  • OFPT_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
  • OFPT_FEATURES_REPLY
    • 交换机47310端口（这是我的特征信息，请查收）--->控制器6633端口
  • OFPT_PACKET_IN
    • 交换机47310端口（有数据包进来，请指示）--->控制器6633端口
  • OFPT_FLOW_MOD
    • 控制器通过6633端口向交换机47310端口下发流表项，指导数据的转发处理
  • OFPT_PACKET_OUT
    • 控制器6633端口（请按照我给你的action进行处理）--->交换机47310端口
  • 相关交互图
  1. 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？
    答：交换机与控制器建立通信时使用TCP协议

（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。
  • OFPT_HELLO
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;
};


HELLO报文的四个参数和代码相对应

  • OFPT_FEATURES_REQUEST
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. */
};
  • OFPT_SET_CONFIG
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. */
};

  • OFPT_PORT_STATUS
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;
};

  • OFPT_FEATURES_REPLY
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. */
};

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. */
};

  • OFPT_PACKET_IN
#交换机查找流表，发现没有匹配条目时
enum ofp_packet_in_reason {
    OFPR_NO_MATCH,          /* No matching flow. */
    OFPR_ACTION             /* Action explicitly output to controller. */
};
#有匹配条目但是对应的action是OUTPUT=CONTROLLER时
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. */
};

  • OFPT_FLOW_MOD
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];
};

  • OFPT_PACKET_OUT
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、实验心得

实验过程中抓包后寻找所需的数据报文需要一定的耐心，为避免在寻找中途出现卡机的现象，最好先把抓包结果保存下来，这样不至于出现错误要重新抓包重新截图。要看懂OpenFlow源码比较困难，所以只能对照抓包结果和老师给的pdf大致了解一下OpenFlow主要消息类型对应的数据结构的定义。这次实验没有碰到什么问题，按部就班做下来非常顺利。通过这次实验我学会了分析wireshark抓的通信数据包并由此更直观地了解到OpenFlow协议中交换机和控制器的消息交互过程。

posted @ 2021-09-27 21:47  POOH_BEAR  阅读(41)  评论(0)  编辑  收藏  举报