标签：struct OpenFlow 端口实践 header ofp uint16 交换机 SDN

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。

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（我最高能支持OpenFlow 1.0） ---> 交换机50002端口

交换机50002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50002端口

Set Conig
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50002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50002端口（这是我的特征信息，请查收） ---> 控制器6633端口

Packet_in
• 有两种情况： • 交换机查找流表，发现没有匹配条目时
• 有匹配条目但是对应的action是OUTPUT=CONTROLLER时
交换机50002端口（有数据包进来，请指示）--- 控制器6633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50002端口、交换机50002端口
下发流表项，指导数据的转发处理（发现少抓了一张，这里重做了）

Packet_out
控制器6633端口（请按照我给你的action进行处理） ---> 交换机50002端口

3.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？ TCP

（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。
1.header（每个都有）

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. */
};
OFP_ASSERT(sizeof(struct ofp_header) == 8);

2.hello

struct ofp_hello {
    struct ofp_header header;
};

3.Features Request(好像和Hello一样)

struct ofp_hello {
    struct ofp_header header;
};

4.Set Conig

enum ofp_config_flags {
    /* Handling of IP fragments. */
    OFPC_FRAG_NORMAL   = 0,  /* No special handling for fragments. */
    OFPC_FRAG_DROP     = 1,  /* Drop fragments. */
    OFPC_FRAG_REASM    = 2,  /* Reassemble (only if OFPC_IP_REASM set). */
    OFPC_FRAG_MASK     = 3
};

/* 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. */
};
OFP_ASSERT(sizeof(struct ofp_switch_config) == 12);

5.port_state

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;
};
OFP_ASSERT(sizeof(struct ofp_port_status) == 64);

6.Features Reply

struct ofp_switch_features {
    struct ofp_header header;
    uint64_t datapath_id;   
    uint32_t n_buffers;    
    uint8_t n_tables;       
    uint8_t pad[3];        
    /* Features. */
    uint32_t capabilities; /
    uint32_t actions;      
    /* Port info.*/
    struct ofp_phy_port ports[0];  
};
OFP_ASSERT(sizeof(struct ofp_switch_features) == 32);

7.Packet_in

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);

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. */
};
OFP_ASSERT(sizeof(struct ofp_flow_mod) == 72);

9.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.) */
};
OFP_ASSERT(sizeof(struct ofp_packet_out) == 16);

（三）实验总结

整体难度比以往简单很多，做得很快，但我flow_mod发现少截了一张导致得在做一遍... ，然后记得先开抓包，在建拓扑，抓包的右边有名字。好好看ppt，可以少走很多弯路，例如数据结构在哪看，这个我也卡一会。
这次实验最大的困难还是自己没检查好，浪费了不少时间，没有仔细看ppt，下次要多注意一下，争取别在犯错。
通过这次实验，我对openflow协议数据交互过程有了更深的了解，也对前面的操作进行了一定的复习，有很多收获，希望下次实验自己能顺利一点。

标签：struct,OpenFlow,端口,实践,header,ofp,uint16,交换机,SDN
From： https://www.cnblogs.com/chenyanzhen/p/16757153.html

SDN OpenFlow协议分析实践