SDN第三次上机作业

Posted 2021-09-21 ....!

实验三：

任务一

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。

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

任务二

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。

1、流程图

2、抓包结果

• HELLO
  
  

• openflow对应的数据结构

/* Header on all OpenFlow packets. */
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);

/* 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/Set Conig
  
  

• openflow对应的数据结构

struct ofp_stats_request {
    struct ofp_header header;
    uint16_t type;              /* One of the OFPST_* constants. */
    uint16_t flags;             /* OFPSF_REQ_* flags (none yet defined). */
    uint8_t body[0];            /* Body of the request. */
};
OFP_ASSERT(sizeof(struct ofp_stats_request) == 12);

/* 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);

• Port_Status
  

• openflow对应的数据结构

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

• Features Reply
  

• openflow对应的数据结构

struct ofp_stats_reply {
    struct ofp_header header;
    uint16_t type;              /* One of the OFPST_* constants. */
    uint16_t flags;             /* OFPSF_REPLY_* flags. */
    uint8_t body[0];            /* Body of the reply. */
};
OFP_ASSERT(sizeof(struct ofp_stats_reply) == 12);

• Packet_in
  

• openflow对应的数据结构

/* 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);

• Flow_mod
  

• openflow对应的数据结构

/* 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);

/* Why was this flow removed? */
enum ofp_flow_removed_reason {
    OFPRR_IDLE_TIMEOUT,         /* Flow idle time exceeded idle_timeout. */
    OFPRR_HARD_TIMEOUT,         /* Time exceeded hard_timeout. */
    OFPRR_DELETE                /* Evicted by a DELETE flow mod. */
};

• Packet_out
  

• openflow对应的数据结构

/* 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);

任务三

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？
答：TCP协议

进阶任务

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。

总结

• 本次实验比较简单，抓包分析之前做过，只不过分析的是其他类型的包，但都差不多
• 就是hello一开始找不到，通过请教同学发现要在run之前就要开始抓包
• 看相关的数据结构的时候要通过翻译软件才能看懂各个字段表示什么