實驗3：OpenFlow協議分析實踐

拓撲文件
抓包流程圖
1、hello
55394向6633發送hello包，并且使用openflow1.0

6633向55394發送hello包，并且使用openflow1.0

2、features_request
控制器6633端口（我需要你的特征信息） ---> 交換機55394端口

3、Set Conig
控制器6633端口（請按照我給你的flag和max bytes of packet進行配置） ---> 交換機55394端口

4、Port_Status
當交換機端口發生變化時，告知控制器相應的端口狀態。

5、Features Reply
交換機55394端口（這是我的特征信息，請查收） ---> 控制器6633端口

6、Packet_in
有兩種情況：
交換機查找流表，發現沒有匹配條目時
有匹配條目但是對應的action是OUTPUT=CONTROLLER時，交換機35534端口（有數據包進來，請指示）--- 控制器6633端口

7、Flow_mod
控制器通過6633端口向交換機34286端口、交換機34286端口下發流表項，指導數據的轉發處理

8、Packet_out
控制器6633端口（請按照我給你的action進行處理） ---> 交換機55394端口

9、交互圖
回答問題：交換機與控制器建立通信時是使用TCP協議還是UDP協議？
答：交換機和控制器建立通信時是使用TCP協議
進階作業
1、Hello

struct ofp_header {
    uint8_t version;    /* 版本號OFP_VERSION. */
    uint8_t type;       /* 消息類型One of the OFPT_ constants. */
    uint16_t length;    /* 長度Length including this ofp_header. */
    uint32_t xid;       /* ID 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;
};

2、Features Request

struct ofp_header {
    uint8_t version;    /* 版本號OFP_VERSION. */
    uint8_t type;       /* 消息類型One of the OFPT_ constants. */
    uint16_t length;    /* 長度Length including this ofp_header. */
    uint32_t xid;       /* ID Transaction id associated with this packet.
                           Replies use the same id as was in the request
                           to facilitate pairing. */
};

3、Set Config

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
};//不同flag代表不同的處理方式

/* Switch configuration. */
struct ofp_switch_config {
    struct ofp_header header;
    uint16_t flags;             /*用來指示交換機如何處理 IP 分片數據包 OFPC_* flags. */
    uint16_t miss_send_len;     /* 用來指示當一個交換機無法處理的數據包到達時，將數據包發給控制器的最大字節數。Max bytes of new flow that datapath should
                                   send to the controller. */
};
OFP_ASSERT(sizeof(struct ofp_switch_config) == 12);

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;
};
OFP_ASSERT(sizeof(struct ofp_port_status) == 64);
//這個是當交換機端口發生變化時，告知控制器相應的端口狀態,發生變化包括增加、刪除、修改物理端口，則需發送port status來告知

5、Features Reply

/* Switch features. */
struct ofp_switch_features {
    struct ofp_header header;
    uint64_t datapath_id;   /* 唯一標識ID號Datapath unique ID.  The lower 48-bits are for
                               a MAC address, while the upper 16-bits are
                               implementer-defined. */

    uint32_t n_buffers;     /*緩沖區可緩存的最大數據包個數 Max packets buffered at once. */

    uint8_t n_tables;       /* 流表數量Number of tables supported by datapath. */
    uint8_t pad[3];         /* Align to 64-bits. */

    /* Features. */
    uint32_t capabilities;  /*支持的特殊功能Bitmap of support "ofp_capabilities". */
    uint32_t actions;       /* 支持的動作 Bitmap of supported "ofp_action_type"s. */

    /* Port info.*/
    struct ofp_phy_port ports[0];  /*物理端口描述列表 Port definitions.  The number of ports
                                      is inferred from the length field in
                                      the header. */
};
OFP_ASSERT(sizeof(struct ofp_switch_features) == 32);

6、Packet_in

/* Packet received on port (datapath -> controller). */
struct ofp_packet_in {
    struct ofp_header header;
    uint32_t buffer_id;     /*Packet-in消息所攜帶的數據包在交換機緩存區中的ID ID assigned by datapath. */
    uint16_t total_len;     /* data字段的長度Full length of frame. */
    uint16_t in_port;       /* 數據包進入交換機時的端口號Port on which frame was received. */
    uint8_t reason;         /*發送Packet-in消息的原因 Reason packet is being sent (one of OFPR_*) */
    uint8_t pad;
    uint8_t data[0];        /*攜帶的數據包  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);

7、Flow_mod

/* Flow setup and teardown (controller -> datapath). */
struct ofp_flow_mod {
    struct ofp_header header;
    struct ofp_match match;    /* 流表的匹配域 Fields to match */
    uint64_t cookie;            /*流表項標識符 Opaque controller-issued identifier. */

    /* Flow actions. */
    uint16_t command;            /* 可以是ADD,DELETE,DELETE-STRICT,MODIFY,MODIFY-STRICTOne of OFPFC_*. */
    uint16_t idle_timeout;        /*空閑超時時間 Idle time before discarding (seconds). */
    uint16_t hard_timeout;       /* 最大生存時間 Max time before discarding (seconds). */
    uint16_t priority;            /*優先級，優先級高的流表項優先匹配 Priority level of flow entry. */
    uint32_t buffer_id;           /*緩存區ID ,用于指定緩存區中的一個數據包按這個消息的action列表處理 Buffered packet to apply to (or -1).
                                     Not meaningful for OFPFC_DELETE*. */
    uint16_t out_port;            /*如果這條消息是用于刪除流表則需要提供額外的匹配參數 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;               /*標志位，可以用來指示流表刪除后是否發送flow‐removed消息，添加流表時是否檢查流表重復項，添加的流表項是否為應急流表項。 One of OFPFF_*. */
    struct ofp_action_header actions[0];   /* action列表The action length is inferred
                                            from the length field in the
                                            header. */
};
OFP_ASSERT(sizeof(struct ofp_flow_mod) == 72);

8、Packet_out

/* Send packet (controller -> datapath). */
struct ofp_packet_out {
    struct ofp_header header;
    uint32_t buffer_id;           /*交換機緩存區id，如果為-1則指定的為packet-out消息攜帶的data字段 ID assigned by datapath (-1 if none). */
    uint16_t in_port;            /* 如果buffer_id為‐1，并且action列表中指定了Output=TABLE的動作,in_port將作為data段數據包的額外匹配信息進行流表查詢Packet's 
                                    input port (OFPP_NONE if none). */
    uint16_t actions_len;        /*action列表的長度，可以用來區分actions和data段  Size of action array in bytes. */
    struct ofp_action_header actions[0];  /*動作列表 Actions. */
    /* uint8_t data[0]; */     /*數據緩存區，可以存儲一個以太網幀，可選   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);

個人總結
本次實驗主要是學會了能夠運用 wireshark 對 OpenFlow 協議數據交互過程進行抓包，用抓包軟件獲取控制器與交換機之間的通信數據包。能夠借助包解析工具，分析與解釋 OpenFlow協議的數據包交互過程與機制。進階實驗主要是對源代碼進行分析，這個花費了較多時間去了解，在實驗過程中遇到的問題，通過詢問同學以及查找資料也學習到了很多知識，并且本次實驗讓我對wireshark抓包的使用更加的熟練。

發表于 2022-10-06 11:14 青青子衿l 閱讀(24) 評論(0) 收藏舉報

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實驗3：OpenFlow協議分析實踐

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