2021 SDN实验3：OpenFlow协议分析实践

2024-02-07 23:52:25

实验3：OpenFlow协议分析实践

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

· 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。

· 所创建拓扑结构中有两个交换机，以其中端口号为35242的交换机为例。

Hello

· 控制器6633端口（我最高能支持OpenFlow 1.0） ---> 交换机35242端口

· 交换机35242端口（我最高能支持OpenFlow 1.3）--- 控制器6633端口

· OpenFlow协议向下兼容，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35242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35242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35242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35242端口、交换机35264端口下发流表项，指导数据的转发处理

· 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，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？
通过wireshark抓包工具，可一看出使用的是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。

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;
};

Features_Request:

· Features_Request消息类型的格式与Hello一致，含有一个头部ofp_header。

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. */
};

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;
};

Features_Reply:

/* 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. */
};
OFP_ASSERT(sizeof(struct ofp_phy_port) == 48);

/* 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. */
};

Packet_IN:

PACKET_IN有两种情况：
· 交换机查找流表，发现没有匹配条目,但是这种包没有抓到过

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. */
};
OFP_ASSERT(sizeof(struct ofp_packet_in) == 20)

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

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. */
};
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）实验报告

⚪ 实验难度：适中
· 本次实验在于利用wireshark抓包工具，获取OpenFlow协议数据包，然后分析各种数据包的用途，分析控制器与交换机的交互关系。进阶实验通过查看源码，验证自己所抓取的数据包。

⚪ 实验过程遇到的困难：
· 问题1：打开wireshark后创建拓扑，过滤Openflow数据包，并未找到Flow_Mod数据包
解决：阅读文档，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，于是启动wireshark后尝试执行pingall，找到了Flow_mod数据包。
· 问题2：保存wireshark抓包文件后，再用wireshark打开.pcapng文件，权限不足。
解决：输入命令行"sudo chmod 777 xxx.pcapng"解决此问题，777代表，user,group ,others ,都有读写和可执行权限。

⚪ 收获与感想：
· 收获：能够熟悉运用 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；对拓扑建立使用到的协议和数据交互流程有了更深的理解；更加熟悉了mininet的一些命令行操作；。
· 感想：本次实验难度不大，通过wireshark抓取数据包、抓取数据包学习了OpenFlow协议下控制器和交换机的交互过程，涉及到多个不同用途的数据包，分析这些数据包的版本、类型、源端口、目的端口和相关字段。截图、源码很多，整理实验报告，画流程图很花实践，但再过程中可以加深对控制器与交换机交互过程的理解。实验任有疏漏，还需要继续补缺！。。。

码农公寓

实验3：OpenFlow协议分析实践

一、实验目的

二、实验环境

三、实验要求

（一）基本要求

Hello

Features_Request:

Set Config:

Port_Status:

Features_Reply:

Packet_IN:

Packet_Out:

Flow_Mod:

（二）进阶要求

Hello

Features_Request:

Set Config:

Port_Status:

Features_Reply:

Packet_IN:

Packet_Out:

Flow_Mod:

（三）实验报告

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