实验内容

（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) 到交换机60984端口
  
  交换机60984端口（我最高能支持OpenFlow 1.5）到控制器6633端口
  
  于是双方建立连接，并使用OpenFlow 1.0

• OFPT_FEATURES_REQUEST
  控制器6633端口（我需要你的特征信息）到交换机60984端口
  

• OFPT_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）到交换机60984端口
  

• OFPT_PORT_STATUS
  控制器6633端口到交换机60984端口，请求特征信息
  

• OFPT_FEATURES_REPLY：
  交换机60984端口到控制器6633端口，回复特征信息
  

• OFPT_PACKET_IN：
  交换机60984端口（有数据包进来，请指示）->控制器6633端口
  

• OFPT_FLOW_MOD：
  分析抓取的flow_mod数据包，控制器通过6633端口向交换机60984端口下发流表项，指导数据的转发处理
  

• OFPT_PACKET_OUT：
  控制器6633端口向交换机60984端口发送数据，并告知交换机输出到1端口
  
  流程图：
  

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协议

（二）进阶要求

• 通用字段

/* 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. */
};

• hello
  

/* 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;
};

交换机或者控制器首先发送hello报文，确认openflow通信版本，对方收到协议后，回复一个hello报文，协商版本。

• Features Request
  

struct ofp_hello {
    struct ofp_header header;
};

控制器发送此报文，查看交换机具体信息

• 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. */
};

flags:告知交换机如何处理IP分片，正常、丢弃还是重组

• Port_Status
  

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_phy_port {
    uint16_t port_no;
    uint8_t hw_addr[OFP_ETH_ALEN];
    char name[OFP_MAX_PORT_NAME_LEN]; /* Null-terminated */

    uint32_t config;        /* Bitmap of OFPPC_* flags. */
    uint32_t state;         /* Bitmap of OFPPS_* flags. */

    /* Bitmaps of OFPPF_* that describe features.  All bits zeroed if
     * unsupported or unavailable. */
    uint32_t curr;          /* Current features. */
    uint32_t advertised;    /* Features being advertised by the port. */
    uint32_t supported;     /* Features supported by the port. */
    uint32_t peer;          /* Features advertised by peer. */
};
OFP_ASSERT(sizeof(struct ofp_phy_port) == 48);

/* 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. */
};

datapath id 数据通道标识符，用来表示交换机的身份。在每一个控制器中独一无二。
n_buffers 一次最多缓存的数据包数量，即交换机自己的缓存能力。
n_tables 表示交换机支持的流表数量。
capabilities 交换机端口所支持的功能,有流表，端口，STP，队列，ARP等。
actions 交换机所支持的actions，有转发和修改包头两种。
port 交换机连接的端口消息。端口MAC地址，链路数据等。

• Packet_in
  

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. */
};

buffer_id packet-in消息所携带的数据包在交换机中的缓存ID。
Total_len 帧的长度。
In_port 数据包进入交换机的入端口号。
Reason packet-in事件的产生原因,分为两种：OFPR_NO_MATCH和OFPR_ACTION。
data 需要处理的未知数据包。

• Packet_out

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];
};
OFP_ASSERT(sizeof(struct ofp_action_header) == 8);

/* 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.) */
};

actions_len：动作信息长度

• Flow_mod
  

struct ofp_match {
    uint32_t wildcards;        /* Wildcard fields. */
    uint16_t in_port;          /* Input switch port. */
    uint8_t dl_src[OFP_ETH_ALEN]; /* Ethernet source address. */
    uint8_t dl_dst[OFP_ETH_ALEN]; /* Ethernet destination address. */
    uint16_t dl_vlan;          /* Input VLAN id. */
    uint8_t dl_vlan_pcp;       /* Input VLAN priority. */
    uint8_t pad1[1];           /* Align to 64-bits */
    uint16_t dl_type;          /* Ethernet frame type. */
    uint8_t nw_tos;            /* IP ToS (actually DSCP field, 6 bits). */
    uint8_t nw_proto;          /* IP protocol or lower 8 bits of
                                * ARP opcode. */
    uint8_t pad2[2];           /* Align to 64-bits */
    uint32_t nw_src;           /* IP source address. */
    uint32_t nw_dst;           /* IP destination address. */
    uint16_t tp_src;           /* TCP/UDP source port. */
    uint16_t tp_dst;           /* TCP/UDP destination port. */
};

/* 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. */
};

flow_mod是openflow协议核心消息之一，作用是下发流表项。

个人总结

本次实验难度不大，按照实验流程就能进行，但在实验中还是遇到了一些小问题，比如刚开始抓包时总是抓不到openflow协议的包，上网得知要先sudo wireshark才能抓到。如果要抓到flow_mod消息的包，就要开启CLI，pingall后才会看到。进阶部分代码较多，锻炼了我的阅读能力。通过这次实验，我感受到了传统网络和sdn的差别，了解了OpenFlow协议在控制器和交换机之间的交互流程。