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。
    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
  • 配置好主机 IP 地址导出
  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。
  • hello

    控制器 6633 端口(我最高能支持OpenFlow 1.0)---> 交换机 60450 端口

    交换机 60450 端口(我最高能支持 OpenFlow 1.5)---> 控制器 6633 端口

    于是双方建立连接,并使用 OpenFlow 1.0

  • Features Request / Set Config

    控制器 6633 端口(我需要你的特征信息)---> 交换机 60450 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 60450 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 60450 端口(这是我的特征信息,请查收)---> 控制器 6633 端口

  • 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 60450 端口(有数据包进来,请指示)---> 控制器 6633 端口

    分析抓取的数据包,可以发现是因为交换机发现此时自己并没有匹配的流表(Reason: No matching flow (table-miss flow entry) (0)),所以要问控制器如何处理

  • Flow_mod

    控制器通过 6633 端口向交换机 60450 端口下发流表项,指导数据的转发处理

    控制器通过 6633 端口向交换机 60452 端口下发流表项,指导数据的转发处理

  • Packet_out

    控制器 6633 端口 (请按照我给你的 action 进行处理)---> 交换机 60450 端口

  • 流程图

  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?
    通过抓取的报文分析可知使用的是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。
  • 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;
    };
    

  • FEATURES_REQUEST

  • 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. */
    };
    

    头部信息 ofp_header header 加上 flags 和 miss_send_len

  • Features Reply

    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. */
    };
    

  • 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;
    };
    

  • 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. */
    };
    
  • 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];
    };
    

  • 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.)   */
    };
    

(三)个人总结

  • 这次实验难度适中,建立拓扑、设置 IP地址都是前面学习过的知识。
  • 学习使用了抓包工具 wireshark,通过过滤器过滤报文。
  • 通过报文与源码之间的比照,可以清楚地知道报文各个字段的构成。
  • 对 SDN 的数据平面与控制平面的解耦合有了更进一步的了解。
  • 实验中遇到的困难
    • 一开始过滤报文时,找不到交换机发出的 hello 报文;后来修改了几次过滤条件找到了交换机发出的 hello 报文。
    • 找不到 Flow_mod 报文,通过命令行发出 ping 命令来发出 Flow_mod 报文。
    • Port_Status 报文,通过修改保存的拓扑 py 文件内的主机与交换机的连接端口实现。
posted @ 2021-09-28 19:24  Coleman_huang  阅读(20)  评论(0编辑  收藏  举报