实验3：OpenFlow协议分析实践

（一）基本要求

HELLO：互相发送Hello消息互相协商Openflow协议版本

控制器6633端口（我最高能支持OpenFlow 1.0） ---> 交换机35220端口

交换机35220端口（我最高能支持OpenFlow 1.4） ---> 控制器6633端口

于是双方建立连接，并使用OpenFlow 1.0

Features Request：控制器向将交换机发送Featrues Request消息，获取交换机特征信息

控制器6633端口---> 交换机35220端口

Set Conig：控制器告诉交换机如何配置

控制器6633端口---> 交换机35220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。

交换机35220端口---> 控制器6633端口

Features Reply：Featrues Request的回复的交换机的特征信息

交换机35220端口---> 控制器6633端口

Packet_in：交换机收到数据包后问控制器如何处理

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是控制器时

交换机35220端口---> 控制器6633端口

Flow_mod：分析抓取的flow_mod数据包，控制器向交换机下发流表项，指导数据的转发

控制器通过6633端口向交换机35220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35222端口下发流表项，指导数据的转发处理


Packet_out：告诉交换机将数据输出到交换机的哪个端口

控制器6633端口---> 交换机35220端口

流程图

TCP协议

TCP为Transmission Control Protocol的缩写

（二）进阶 OpenFlow主要消息类型对应的数据结构定义

OpenFlow的数据包头通用字段

/* 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);

消息类型

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 */

};

hello和features request


/* 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;
};

features reply

/* Switch features. */
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. */
};
OFP_ASSERT(sizeof(struct ofp_switch_features) == 32);

set config

enum ofp_config_flags {
    /* Handling of IP fragments. */
    OFPC_FRAG_NORMAL   = 0,  /* No special handling for fragments. */
    OFPC_FRAG_DROP     = 1,  /* Drop fragments. */
    OFPC_FRAG_REASM    = 2,  /* Reassemble (only if OFPC_IP_REASM set). */
    OFPC_FRAG_MASK     = 3
};

/* 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. */
};
OFP_ASSERT(sizeof(struct ofp_switch_config) == 12);

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;
};
OFP_ASSERT(sizeof(struct ofp_port_status) == 64);

packet_in

/* Why is this packet being sent to the controller? */
enum ofp_packet_in_reason {
    OFPR_NO_MATCH,          /* No matching flow. */
    OFPR_ACTION             /* Action explicitly output to controller. */
};

/* Packet received on port (datapath -> controller). */
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

enum ofp_flow_mod_flags {
    OFPFF_SEND_FLOW_REM = 1 << 0,  /* Send flow removed message when flow
                                    * expires or is deleted. */
    OFPFF_CHECK_OVERLAP = 1 << 1,  /* Check for overlapping entries first. */
    OFPFF_EMERG         = 1 << 2   /* Remark this is for emergency. */
};

/* Flow setup and teardown (controller -> datapath). */
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. */
};
OFP_ASSERT(sizeof(struct ofp_flow_mod) == 72);

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.) */
};
OFP_ASSERT(sizeof(struct ofp_packet_out) == 16);

个人总结

  • 先抓包再运行python文件生成拓扑
  • 通过过滤器输入openflow_v*过滤数据报文的时候，pdf只说了1 4，但是随着版本更新，也可以是 5 6，比如我的交换机发给控制器的hello包支持到openflow 1.4，这个时候过滤器输入openflow_v5才能过滤出来
  • 发现找不到Features Request的源码，对比抓包信息后，发现和hello的格式一模一样，因此猜测是同一个源码（跟同学讨论了一下，好像猜对了捏）
  • Flow_mod为控制器指导交换机转发发送的数据包，根据这个可知，再Mininet CLI中pingall就可出现然后被捕获
  • 了解了OpenFlow协议中交换机与控制器的消息交互过程，了解了wireshark 抓包后的信息大概表示什么内容
posted @ 2022-09-27 14:17  计科废物1  阅读(112)  评论(0)  编辑  收藏  举报
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