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实验3 OpenFlow协议分析实践

时间：2022-09-27 20:14:21浏览次数：37  
标签：struct OpenFlow 实践 header ofp 交换机 实验 action

实验3 OpenFlow协议分时实践

基础实验

抓包分析

step1：搭建拓扑并配置相应IP
image
IP配置如下：
image
step2：
Pingall并抓包
image
step3：分析
（1）hello包
image
表示含义：控制器6633端口 发送“我最高能支持OpenFlow1.0”信息给交换机38200端口
image
表示含义：交换机端口38200发“我最高能支持OpenFlow1.0”信息给控制器的6633端口
于是双方建立连接，并使用OpenFlow1.0

（2）Feature_Request
image
表示含义：控制器6633端口发送“我需要你的特征信息”信息给交换机的38200端口
（3）Set_Config
image
表示含义：控制器6633端口发送信息“请按照我给你的Flag和Max_Bytes of Packet进行配置"信息给交换机的38200端口
（4）Feature_Reply
image
表示含义：交换机38200端口发送“这是我的特征信息，请查收”信息给控制器的6633端口
（5）Packet_in
image
表示含义：交换机38200端口发送“有数据包进入，请指示”信息给控制器的6633端口
（6）Packet_out
image
表示含义：控制器6633端口发送“请按照我给你的action进行处理”信息给交换机的38200端口
（7）Flow_Mod
image
表示含义：控制器通过6633端口向交换机38198端口下发流表项，指导数据的转发处理。
（8）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
image

交互图

image

问题回答

交换机与控制器建立通信时是使用TCP协议还是UDP协议？
TCP协议

进阶要求

查看OpenFlow目录下的头文件
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. */
};

物理描述端口


/* 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. */
};

交换机的特性

/* 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. */
};

n_buffers表示交换机缓冲区可以
缓存的最大数据包个数
n_tables表示流表数量
pad作为一个填充值
capabilities表示支持的特殊功能
actions:表示支持的动作
port data表示物理端口描述列表

(1)hello

/* 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);

/* 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;
};

image
（2）Feature Request

/* 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. */
};

image
(3) 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. */
};

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
image
图中所示为交换机不知道如何处理数据包因而发送信息给控制器
（4）Flow_mod

/* 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. */
};

image
(5)Packet_mod

/* Action header that is common to all actions.  The length includes the
 * header and any padding used to make the action 64-bit aligned.
 * NB: The length of an action *must* always be a multiple of eight. */
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];
};
OFP_ASSERT(sizeof(struct ofp_action_header) == 8);

/* Send packet (controller -> datapath). */
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.) */
};

(6) Packet_out
"请按照我给你的action进行处理"

/* Action header that is common to all actions.  The length includes the
 * header and any padding used to make the action 64-bit aligned.
 * NB: The length of an action *must* always be a multiple of eight. */
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];
};
OFP_ASSERT(sizeof(struct ofp_action_header) == 8);

/* Send packet (controller -> datapath). */
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.) */
};

image

实验总结

（1）此次实验的整体过程
在OpenFlow1.3协议的情况下，控制器与OpenFlow交换机的消息完整交互流程如下：
1、 控制器与OpenFlow交换机通过TCP“三次握手”，建立有效的连接。其中，控制器一端的端口号为6633。
2、 控制器与OpenFlow交换机之间相互发送Hello消息，用于协商双方的OpenFlow版本号。在双方支持的最高版本号不一致的情况下，协商的结果将以较低的OpenFlow版本为准。
3、 控制器向OpenFlow交换机发送Features Request消息，请求OpenFlow交换机上传自己的详细参数。OpenFlow交换机收到请求后，向控制器发送Features Reply消息，详细汇报自身参数，包括支持的buffer数目、流表数以及Actions等。
4、 控制器通过Set Config消息下发配置参数，然后通过Get config Request消息请求OpenFlow交换机上传修改后的配置信息。OpenFlow交换机通过Get config Reply消息向控制器发送当前的配置信息。
5、 控制器与OpenFlow交换机之间发送Packet_out、Packet_in消息，通过Packet_out中内置的LLDP包，进行网络拓扑的探测。
6、 控制器与OpenFlow交换机之间通过发送Multipart Request、Mutipart Reply消息，控制器能获取OpenFlow交换机的状态信息，包括流的信息、端口信息等。
7、 控制器与OpenFlow交换机之间通过发送Echo Request、Echo Reply消息，保证二者之间存在有效连接，避免失联。
（2）心得
此次实验，我学习了OpenFlow的协议形式，当交换机不知道如何处理数据包时，会上报给控制器，由控制器指示所需执行的action，加深了我对软件定义网络的理解。

标签：struct,OpenFlow,实践,header,ofp,交换机,实验,action
From： https://www.cnblogs.com/hhhf/p/16732783.html

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