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实验3 OpenFlow协议分时实践

时间:2022-09-28 16:58:57浏览次数:42  
标签:struct OpenFlow 端口 实践 header ofp uint16 实验 port

基础实验

抓包分析

step1:搭建拓扑并配置相应IP

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43826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43826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43826端口
(4)Feature_Reply

image

表示含义:交换机43826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43826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43826端口

(7)Flow_Mod

 

 

 

表示含义:控制器通过6633端口向交换机43836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。

 

 

 

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

HELLO

OpenFlow的数据包头通用字段
image

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. */
};

  

HELLO报文的四个参数

FEATURES_REQUEST

image

源码参数格式与HELLO相同,与上述ofp_header结构体中数据相同

SET_CONFIG

image
控制器下发的交换机配置数据结构体

/* 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. */
};

 

PORT_STATUS

image

/* 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;
};

 

FEATURES_REPLY

image

/* 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. */
};
/* 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. */
};

 

可以看到与图中信息一一对应,包括交换机物理端口的信息

PACKET_I

在控制器获取完交换机的特性之后 , 交换机开始处理数据。

 

 

 

/* 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. */
};

 

OFPT_PACKET_OUT

控制器可以使用PacketOut消息,告诉交换机某一个数据包如何处理。

 

 

/* 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.) */
};

 

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. */
};
/* 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];
};

 

(三)实验总结
本次实验使用wireshark进行抓包以及对抓包结果进行分析制作流程图
清除拓扑结构再运行sudo mininet/examples/miniedit.py 搭建拓扑,进行设置和配置,export文件。另起一个终端运行wireshark,再运行拓扑结构,pingall得到想要的结果。

在进行抓包时必须一次性完成所有包的查找分析,否则再次启动虚拟机时,会发生两次抓包同一个包而端口不一致的情况。

通过本次实验,我能够熟练地运用 wireshark 对 OpenFlow 协议数据交互过程进行抓包。认识到controller和switches通信是通过TCP协议,建立起可靠传输,里面包裹openflow协议。对 OpenFlow 协议的数据包交互过程与机制有了更深入的了解。通过和源码对照,能够直观的认识到不同类型的数据报的组成,以及各字段所代表的意义和作用。

标签:struct,OpenFlow,端口,实践,header,ofp,uint16,实验,port
From: https://www.cnblogs.com/cyd051701128/p/16738666.html

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