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

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。

主机	IP地址
h1	192.168.0.101/24
h2	192.168.0.102/24
h3	192.168.0.103/24
h4	192.168.0.104/24

ip和拓扑

2、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。

Hello

控制器6633端口（支持Open Flow1.0） ---> 交换机52032端口

交换机54892端口（支持Open Flow1.5）---> 控制器6633端口

OFPT_HELLO后，双方建立连接使用openflow1.0协议

FEATURES_REQUEST

控制器6633端口（我需要你的特征信息） ---> 交换机52032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52032端口

PORT_STATUS

从交换机52032端口到控制器6633端口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

交换机端口52032（这是我的特征信息，请查收） ——> 控制器6633端口

Packet_In

交换机52032端口（有数据包进来，请指示） ——> 控制器6633端口

PACKET_OUT

控制器6633端口（请按照我给你的action进行处理） ---> 交换机52032端口:

Flow_Mod

分析抓取的flow_mod数据包，控制器通过6633端口向交换机52032端口下发流表项，指导数据的转发处理

3.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。

4.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，可看出使用的是TCP协议（Transmission Control Protocol）

（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，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;
};

可以看到对应了HELLO报文的四个参数与之一一对应

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;
};

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

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

/* 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. */
};

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.) */
};

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];
};

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。
本次实验的操作难度不大，我们只需注意搭建拓扑时修改好响应的网段与ＩＰ地址即可，但所需验证的理论知识多，所以本次实验的难度还是较大。

实验过程遇到问题：

问题1：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1：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。
问题2：在一开始抓包的时候，我只用openflow_v1时找不到52032对6633端口发送的hello
解决2：后来上网查询以及询问同学，我改用openflow_v6成功获取了信息。

posted @ 2022-09-28 12:04 ww_here 阅读(52) 评论(0) 收藏举报

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wwhere

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

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。

ip和拓扑

2、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。

Hello

FEATURES_REQUEST

SET_CONFIG

PORT_STATUS

Features Reply

Packet_In

PACKET_OUT

Flow_Mod

3.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

4.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？

（二）进阶要求

Hello

FEATURES_REQUEST

SET_CONFIG

PORT_STATUS

Features Reply

Packet_In

PACKET_OUT

Flow_Mod

个人总结

实验过程遇到问题：

公告