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

Ubuntu 20.04 Desktop amd64

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。

2.查看抓包结果

OFPT_HELLO

控制器6633端口(我最高能支持OpenFlow 1.0) ---> 交换机53222端口:

交换机53222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

OFPT_FEATURES_REQUEST

控制器6633端口(我需要你的特征信息) ---> 交换机53222端口

OFPT_SET_CONFIG

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53222端口:

OFPT_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

OFPT_FEATURES_REPLY

交换机53222端口(这是我的特征信息,请查收) ---> 控制器6633端口

OFPT_PACKET_IN

交换机53222端口(有数据包进来,请指示)--- 控制器6633端口

OFPT_PACKET_OUT

控制器6633端口(请按照我给你的action进行处理) ---> 交换机53222端口

OFPT_FLOW_MOD

分析抓取的flow_mod数据包,控制器通过6633端口向交换机53222端口、交换机53224端口下发流表项,指导数据的转发处理

画出相关交互图或流程图

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?

答:TCP协议,如图。

(二)进阶要求:将抓包基础要求第2步的抓包结果对照OpenFlow源码

OpenFlow的数据包头具有通用字段,相关数据结构定义如下:

/* 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

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;
};

OFPT_FEATURES_REQUEST

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;
};

OFPT_SET_CONFIG

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. */
};

OFPT_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;
};

OFPT_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. */
    };

OFPT_PACKET_IN

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

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.) */
};

OFPT_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. */
};

四、个人总结

  1. 遇到的问题以及解决方案:
    需要先sudo wireshark再建立拓扑 才能抓到OpenFlow协议的数据包。后来发现,然后就顺利抓到包了。后来发现也找不到OFPT_FLOW_MOD数据包。在同学的指引下,要进行CLI中pingall,才找到这个数据包。
  2. 收获与感想:
    个人感觉本次实验难度很大,要跟随老师操作也要在同学的帮助下一步一步完成。
    通过本次实验,我学到了如何使用wireshark抓取OpenFlow协议的数据包,同时有了一定的了解对OpenFlow协议中交换机与控制器的消息交互过程,对数据包交互也有了更深地理解。在进阶要求中,通过比对openflow.h源码与抓取到的数据包的结构,对OpenFlow主要消息类型对应的数据结构定义有了更深刻的理解。本次实验收获很多。
posted @ 2022-09-27 23:14  念烨  阅读(28)  评论(0编辑  收藏  举报