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。
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
  1. 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 Conig

Port_Status

Features Reply

Packet_in

Flow_mod

Packet_out

流程图：

  1. 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？
    SDN交换机和控制器在建立TCP连接的基础上进行通信

（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
OpenFlow主要消息类型

点击查看代码 
enum ofp_type {
    /* Immutable messages. */
    OFPT_HELLO,               /* Symmetric message */
    OFPT_ERROR,               /* Symmetric message */
    OFPT_ECHO_REQUEST,        /* Symmetric message */
    OFPT_ECHO_REPLY,          /* Symmetric message */
    OFPT_VENDOR,              /* Symmetric message */

    /* Switch configuration messages. */
    OFPT_FEATURES_REQUEST,    /* Controller/switch message */
    OFPT_FEATURES_REPLY,      /* Controller/switch message */
    OFPT_GET_CONFIG_REQUEST,  /* Controller/switch message */
    OFPT_GET_CONFIG_REPLY,    /* Controller/switch message */
    OFPT_SET_CONFIG,          /* Controller/switch message */

    /* Asynchronous messages. */
    OFPT_PACKET_IN,           /* Async message */
    OFPT_FLOW_REMOVED,        /* Async message */
    OFPT_PORT_STATUS,         /* Async message */

    /* Controller command messages. */
    OFPT_PACKET_OUT,          /* Controller/switch message */
    OFPT_FLOW_MOD,            /* Controller/switch message */
    OFPT_PORT_MOD,            /* Controller/switch message */

    /* Statistics messages. */
    OFPT_STATS_REQUEST,       /* Controller/switch message */
    OFPT_STATS_REPLY,         /* Controller/switch message */

    /* Barrier messages. */
    OFPT_BARRIER_REQUEST,     /* Controller/switch message */
    OFPT_BARRIER_REPLY,       /* Controller/switch message */

    /* Queue Configuration messages. */
    OFPT_QUEUE_GET_CONFIG_REQUEST,  /* Controller/switch message */
    OFPT_QUEUE_GET_CONFIG_REPLY     /* Controller/switch message */

};

Hello

点击查看代码 
/* OFPT_HELLO.  This message has an empty body, but implementations must
 * ignore any data included in the body, to allow for future extensions. */
struct ofp_hello {
    struct ofp_header header;
};

features request源码参数格式与HELLO的一致

features reply

点击查看代码 
/* 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. */
};

port_status

点击查看代码 
/* 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;
};

set_config

点击查看代码 
/* 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. */
};

packet_in

点击查看代码 
/* 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

点击查看代码 
/* 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

点击查看代码 
/* 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. */
};
OFP_ASSERT(sizeof(struct ofp_flow_mod) == 72);

三、总结

1.SDN交换机和控制器在建立TCP连接的基础上，进行如下通信：
a、首先互相发送Hello消息互相协商Openflow协议版本。
b、发送Hello消息之后控制器向将换机发送Featrues Request消息，获取交换机的ID、缓冲区数量、端口信息等特性，因此交换机相应的回Features Reply。
c、set config是控制器用来配置交换机发送的数据包。
d、当流表中没有关于新到达流的数据包或者即使有关于新到达流的流规则但其行为是发往控制器的时候，交换机向控制器发送Packet In消息。
e、而Packet Out消息是控制器指定的某个数据包的处理方法。

2.先开启抓包再构建拓扑

3.features request源码参数格式与HELLO的一致

posted @   X1aomai  阅读(51)  评论(0)  编辑  收藏  举报
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