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实验3:OpenFlow协议分析实践

作者:互联网

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

  1. 下载虚拟机软件Oracle VisualBox;
  2. 在虚拟机中安装Ubuntu 20.04 Desktop amd64,并完整安装Mininet;

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包。
    img
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
  1. 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。

    由于题述拓扑中存在两个交换机,这里只以其中一个交换机与控制器的交互作为说明

    • Hello

      交换机和控制器互相发送Hello报文,控制器默认使用OpenFlow1.0版本,交换机我们先前设置其支持OpenFlow1.0和1.3,这里交换机使用所能支持的最高版本OpenFlow1.3进行通信。最后按照规定两者以较低版本1.0进行通信

      控制器6633端口(我最高能支持OpenFlow 1.0) ---> 交换机33616端口

      image-20210923165106663

      交换机33616端口(我最高能支持OpenFlow 1.3)---> 控制器6633端口

      image-20210923165444509

    • Features Request / Set Config

      控制器向交换机发送FEATURES_REQUEST询问交换机信息

      控制器向交换机发送SET_CONFIG配置相关指标

      控制器6633端口(我需要你的特征信息) ---> 交换机33616端口

      image-20210923170913286

      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33616端口

      image-20210923170951124

    • 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

      image-20210923171423525

    • Features Reply

      交换机收到Features Request之后随即发送Features Reply,将自己的信息发送至控制器

      交换机33616端口(这是我的特征信息,请查收)---> 控制器6633端口

      image-20210923171811570

    • Packet_in

      出现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33616端口(有数据包进来,请指示)--- 控制器6633端口

      image-20210923172148834

    • Packet_out

      控制器6633端口(请按照我给你的action进行处理) ---> 交换机33616端口

      image-20210923172456141

    • Flow_mod

      在该过程中我并未抓取到该类型的数据包

    • 相关交互图

      image-20210923192527064

      由于Features Request / Set Config和Packet_out / Flow_mod没有明显的先后关系所以放在一起

  2. 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?

    使用了TCP协议,抓包截图与topo.py源码中均能体现

    image-20210922221030644

    image-20210923165416855

(二)进阶要求

  1. 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。

    • Hello

      image-20210923194747012

      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. */
      };
      struct ofp_hello {
          struct ofp_header header;
      };
      
    • Features Request

      image-20210923170913286

      可以发现这一个消息类型的格式与Hello一致,含有一个头部ofp_header

    • Set Config

      image-20210923170951124

      /* 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. */
      };
      

      以上可以看出这个消息类型用于控制器向交换机发送配置信息

    • Port_Status

      image-20210923171423525

      /* 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;
      };
      
    • Features Reply

      image-20210923195827138

      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. */
      };
      /* Description of a physical port */
      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. */
      };
      
    • Packet_in

      image-20210923200116321

      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. */
      

      除以上与这种情况外,还有Packet_in数据报还有一种:

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

      image-20210923200417915

      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.) */
      };
      
    • Flow_mod

      由于未找到这种数据包这里只有对应的源码

      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. */
      };
      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];
      };
      

四、个人总结

标签:控制器,struct,uint16,OpenFlow,实践,header,ofp,交换机,实验
来源: https://www.cnblogs.com/beyondzones/p/15327257.html