实验3：OpenFlow协议分析实践

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。

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
  • 构建拓扑，并按要求配置IP地址

  • 配置完毕后将文件保存至031902113/lab3

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。

  • sudo wireshark启动wireshark,选择any模式进行抓包
    Type:OFPT_HELLO 控制器6633端口-->交换机35850端口,协议为openflow1.0

交换机35850端口-->控制器6633端口,协议为openflow1.5

Type:OFPT_FEATURES_REQUEST控制器6633端口-->交换机35850端口,协议为openflow1.0

Type:OFPT_SET_CONFIG控制器6633端口-->交换机35850端口,协议为openflow1.0

Type:OFPT_PORT_STATUS交换机35850端口-->控制器6633端口,协议为openflow1.0

OFPT_FEATURES_REPLY交换机35850端口-->控制器6633端口,协议为openflow1.0

OFPT_PACKET_IN交换机35852端口-->控制器6633端口,协议为openflow1.0

OFPT_PACKET_OUT控制器6633端口-->交换机35852端口,协议为openflow1.0

OFPT_FLOW_MOD控制器6633端口-->交换机35918端口,协议为openflow1.0

  • 本实验中交换机和控制器之间消息交互图

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？
答：交换机与控制器建立通信时使用Transmission Control Protocol为TCP协议。

（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。

1.HELLO源码与对应抓包结果

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;
};

2.FEATURES_REQUEST源码参数格式与HELLO相同,对应抓包结果

3.SET_CONFIG源码与对应抓包结果

/* 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. */
};

4.PORT_STATUS源码与对应抓包结果

/* 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;
};

5.FEATUERS_REPLY源码与对应抓包结果

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. */
};

6.PACKET_IN源码与对应抓包结果

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. */
};

7.PACKET_OUT源码与对应抓包结果

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.) */
};

8.FLOW_MOD源码与对应抓包结果

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];
};

个人总结

遇到的问题一：抓包时只找到了REQUEST和REPLY的包

解决：原因是在运行mininet后才打开wireshark进行抓包，实际上要先打开wireshark进行监测，再运行mininet。

遇到的问题二：抓取的包括DNS协议的包，如何进行筛选？
解决：在wireshark中Apply a display filte中输入openflow_v1或着其他进行筛选。

遇到的问题三：找不到交换机给控制器发送的HELLO报文
解决：当选择openflow_v6时会出现两个交换机给控制器发送的HELLO报文，协议为OpenFlow1.5。

遇到的问题四：为什么最后三种报文的交换机端口都改变了？
解决：这次实验拓扑里有两个交换机，端口会变是因为选的不是同一个交换机的数据包，而FLOW_MOD交换机端口号的改变是因为第一次没找到该报文，而重新做的时候重新给交换机分配了端口号。

实验心得
本次实验在命令输入上较于前两次实验的难度有降低，主要是考验如何使用wireshark进行数据抓包的操作以及需要将openflow源码与抓包结果对应起来。在更加熟悉使用wireshark进行抓包操作的同时，让我更进一步理解交换机和控制器之间消息交互过程，在进阶部分找到的源码可以作进一步的分析，这样可以对OpenFlow协议有更深刻的认识。

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原文地址：https://www.cnblogs.com/rakanXayan/p/15327490.html