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实验3:OpenFlow协议分析实践

作者:互联网

一、实验目的

能够运用 wireshark 对 OpenFlow 协议数据交互过程进行抓包;
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

下载虚拟机软件Oracle VisualBox;
在虚拟机中安装Ubuntu 20.04 Desktop amd64,并完整安装Mininet;
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包。

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
控制器6633端口(我最高能支持OpenFlow 1.0) ---> 交换机51318端口

交换机51320端口(我最高能支持OpenFlow 1.3)--- 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6633端口(我需要你的特征信息) ---> 交换机51318端口

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51318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。

Features Reply
交换机51318端口(这是我的特征信息,请查收)--- 控制器6633端口

Packet_IN:

Packet_Out:

Flow_mod
分析抓取的flow_mod数据包,控制器通过6633端口向交换机51318端口、交换机51320端口下发流表项,指导数据的转发处理

  1. 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。

交互过程:
交换机或控制器首先发送hello报文,确定openflow通信版本。
交换机或控制器收到hello报文之后,回复一个hello报文,协商版本。
控制器发送feature_request报文,查询交换机具体信息。
交换机收到feature_request报文之后,回复feature_reply,报告自己的详细信息给控制器。
工作过程中控制器会不断发送echo_request给交换机,交换机回复echo_reply消息给控制器,确认连接。

  1. 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?
    通过wireshark抓包工具,可看出使用的是TCP协议(Transmission Control Protocol)

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。相关数据结构可在openflow安装目录openflow/include/openflow当中的openflow.h头文件中查询到。
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. */
};

2.FEATURES_REQUEST


与HELLO的代码段一致

3.SET_CONFIG

/* 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. */
};

4.PORT_STATUS

/* 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;
};

5.FEATURES_REPLAY

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

6.PACKET_IN

PACKET_IN有两种情况:
交换机查找流表,发现没有匹配条目,但是本次实验没有抓到这种包

enum ofp_packet_in_reason {
    OFPR_NO_MATCH,          /* No matching flow. */
    OFPR_ACTION             /* Action explicitly output to controller. */
};

有匹配条目,对应的action是OUTPUT=CONTROLLER,固定收到向控制器发送包

/* 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. */
};

7.PACKET_OUT

/* 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.) */
};

8.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. */
};

个人总结:
本次实验难度适中。
本次实验目的在于能够运用 wireshark 对 OpenFlow 协议数据交互过程进行抓包;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。
进阶要求是将抓包结果对照OpenFlow源码,让我们能够了解OpenFlow主要消息类型对应的数据结构定义。
实验过程遇到问题:
问题:打开wireshark后创建拓扑,过滤Openflow数据包,并没有发现Flow_Mod数据包
解决:阅读文档之后,发现Flow_Mod数据包是控制器想交换机下发流表项,指导数据的转发处理,所以在启动wireshark之后,再尝试执行pingall,最后发现了Flow_mod数据包。

标签:struct,OpenFlow,实践,header,ofp,交换机,实验,port
来源: https://www.cnblogs.com/7-days/p/15349841.html