实验3:OpenFlow协议分析实践

实验3:OpenFlow协议分析实践

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。
实验3:OpenFlow协议分析实践
实验3:OpenFlow协议分析实践
实验3:OpenFlow协议分析实践
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
    源端口6633 -> 目的端口46370,从控制器到交换机,协议为openflow1.0
    实验3:OpenFlow协议分析实践
    源端口52458 -> 目的端口6633,从控制器到交换机,协议为openflow1.0
    实验3:OpenFlow协议分析实践

  • FEATURES_REQUEST
    源端口6633 -> 目的端口46370,从控制器到交换机
    实验3:OpenFlow协议分析实践

  • FEATURES_REPLY
    源端口46370 -> 目的端口6633,从交换机到控制器
    实验3:OpenFlow协议分析实践

  • SET_CONFIG
    源端口6633 -> 目的端口46370,从控制器到交换机
    实验3:OpenFlow协议分析实践
    控制器要求交换机按照所给出的信息进行配置

  • OFPT_PORT_STATUS
    源端口46370 -> 目的端口6633,从交换机到控制器
    实验3:OpenFlow协议分析实践
    控制器要求交换机按照所给出的信息进行配置

  • OFPT_PACKET_IN
    源端口46370 -> 目的端口6633,从交换机到控制器
    实验3:OpenFlow协议分析实践
    交换机告知控制器有数据包进来,请求控制器指示

  • OFPT_PACKET_OUT
    源端口6633 -> 目的端口46370,从控制器到交换机
    实验3:OpenFlow协议分析实践
    控制器要求交换机按照所给出的action进行处理

  • OFPT_FLOW_MOD
    源端口6633 -> 目的端口46372,从控制器到交换机
    实验3:OpenFlow协议分析实践
    控制器对交换机进行流表的添加、删除、变更等操作

  • 交互图
    实验3:OpenFlow协议分析实践

(二)进阶要求

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
实验3:OpenFlow协议分析实践

      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;
      };

可以看到,ofp_header结构体内的的version,type,length,xid变量与图中显示的属性一一对应


- FEATURES_REQUEST
实验3:OpenFlow协议分析实践
格式与上述ofp_header结构体中数据相同
- FEATURES_REPLY
实验3:OpenFlow协议分析实践

      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. */
      };
  • SET_CONFIG
    实验3:OpenFlow协议分析实践
      /* 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. */
      };

可以看到源码与图中信息一一对应

  • PORT_STATUS
    实验3:OpenFlow协议分析实践
      /* 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
    实验3:OpenFlow协议分析实践
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
    实验3:OpenFlow协议分析实践
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
    实验3:OpenFlow协议分析实践
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];
};

总结

  本次实验我们使用wireshark抓去网络数据包,验证了在OpenFlow协议下控制器与交换机建立链接与相互交互的过程。本次实验的操作难度不大,我们只需注意搭建拓扑时修改好响应的网段与IP地址即可,但所需验证的理论知识多,所以本次实验的难度还是较大。分析wireshark所抓取的数据包,结合源码分析,使我对OpenFlow协议有了更进一步的了解。实验过程中由于直接使用openflow_v1作为筛选条件,导致我无法看到交换机发送给控制器的hello包,后来发现这个问题时采用openflow_v5抓去该hello信息已经是再一次构建该网络了,所以实验报告中两部分的地址对应不上。

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