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。

进行相关IP配置

2.命令行拓扑完整性测试

3.查看抓包结果
HELLO
控制器6633端口（我最高能支持OpenFlow 1.0） ---> 交换机49154端口

交换机409154端口（我最高能支持OpenFlow 1.5） ---> 控制器6633端口

OFPT_HELLO后，双方协商使用openflow1.0协议

FEATURES_REQUEST
控制器6633端口（我需要你的特征信息） ---> 交换机49154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49154端口

PORT_STATUS
从交换机49154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49154端口到控制器6633端口，回复特征信息

PACKET_IN
交换机49154端口到控制器6633端口（有数据包进来，请指示）

PACKET_OUT
控制器6633端口到交换机49154端口（请按照我给你的action进行处理）

FLOW_MOD
分析抓取的flow_mod数据包，控制器通过6633端口向交换机49154端口、交换机49154端口下发流表项，指导数据的转发处理

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？

如图所示为（Transmission Control Protocol）TCP协议

<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。
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。

1.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. */
};

2.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. */
};

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_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. */
};

6.PACKET_IN
有两种情况：
1.交换机查找流表，发现没有匹配条目。

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

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

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

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

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

遇到的问题
一开始打开抓包时在openflow_v1里没有找到hello数据包，还有后面的一下包也没找到，后来在实验指导ppt里看到老师标记的注意事项里说要先抓包再运行，执行之后便可以找得到对应的数据包。

在寻找FLOW_MOD数据包时，一开始找了很久都没找到，后来试了一下pingall再查找便可以找到。

实验心得

这次实验总体来说不是很难，也没出现什么问题，但是要认真阅读老师给的实验指导书，注意细节。这次实验了解到交换机与控制器建立通信时是使用TCP协，并且了解了OpenFlow主要消息类型对应的数据结构定义。还学会运用 wireshark 对 OpenFlow 协议数据交互过程进行抓包，用过滤器输入“OpenFlow_v1和Openflow_v6”等进行数据包过滤，找出对应的数据包