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。

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:
    控制器与交换机互相发送HELLO消息,可以看到控制器OpenFlow版本为1.0,交换机OpenFlow版本为1.5,依据向下兼容,使用OpenFlow1.0。
    (1)控制器6633端口->交换机55844端口:

(2)交换机55844端口->控制器6633端口:

  • FEATURES_REQUEST/SET_CONFIG:
    (1)控制器6633端口(我需要你的特征信息)->交换机55844端口:

(2)控制器6633端口(请按照我给你的config flag和max bytes of packet进行配置)->交换机55844端口:

  • 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:

  • FEATURES_REPLY:
    交换机55844端口(这是我的特征信息,请查收)->控制器6633端口:

  • PACKET_IN:
    (1)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
    (2)交换机55846(查找的是后面的,所以交换机端口与前面的55844端口略有差异)端口(有数据包进来,请指示)-> 控制器6633端口

分析抓取的数据包,可以看到交换机没有发现自己要匹配的流表:Reason:
No matching flow (table-miss flow entry) (0),所以要询问控制器如何处理。

  • FLOW_MOD:
    分析抓取的flow_mod数据包,控制器通过6633端口向交换机55846端口下发流表项,指导数据的转发处理

  • PACKET_OUT:
    控制器6633端口(请按照我给你的action进行处理)-> 交换机55846端口:输出到交换机的0端口(选择截取的内容有点问题,没有显示端口号)

  • 综上可知,流程图为:

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?
对wireshark的抓包进行分析,可以看出交换器与控制器建立通信时使用的是TCP协议(Transmission Control Protocol)。

(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:

    OpenFlow源码:
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;
};

可以看到对应了HELLO报文的四个参数

  • EATURES_REQUEST:

    可以看到格式与上述ofp_header结构体中数据相同

  • SET_CONFIG:

    OpenFlow源码:

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. */
};
  • PORT_STATUS:

    OpenFlow源码:
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:

    OpenFlow源码:
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. */
};

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. */
};
  • PACKET_IN:

    OpenFlow源码:
/没有匹配/
enum ofp_packet_in_reason {
    OFPR_NO_MATCH,          /* No matching flow. */
    OFPR_ACTION             /* Action explicitly output to controller. */
};
/控制器发送包/
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. */
};
  • FLOW_MOD:

    OpenFlow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];
};
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. */
};
  • PACKET_OUT:

    OpenFlow源码:
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];
};

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.) */
};

四、个人总结

  • 实验难度:较简单

  • 遇到困难及解决办法:
    1、一开始对于先开启抓包再构建拓扑这句话不是很能理解,先开启抓包是要开启到什么程度呢?是要抓包以后再构建拓扑,还是打开拓扑呢?所以便一 一尝试。首先是先构建完拓扑,打开以后再抓包,自然是不行的,找不到hallo,然后是开启抓包再运行拓扑,所幸上次实验已经了解了需要先pinggall,但是还是不行,最后抓包点完any以后再打开之前的拓扑就可以了。
    2、源码太多了,看着别人的源码再一一对照,倒也是找到了,在想有没有一种更快的方法可以进行源码的查找。
    3、后面步骤有一些图片截图的不太好,过两天想重新截取一下,发现重新抓包以后,交换机的端口发生了变化,所以也就直接用之前截取的图片了。

  • 个人感想:
    总的来说,这次实验还是比较简单的,对照老师的PPT找就完事了,不是很费事,就是截图得截取好多,但也还行。自己在代码这块还是得抓紧学习,毕竟没什么基础,争取早日能勉强看懂。

posted @ 2021-09-28 21:51  你^看不见我  阅读(20)  评论(0编辑  收藏  举报