实验3：OpenFlow协议分析实践

（一）基本要求

拓扑文件
wireshark抓包

Hello
控制器6633端口（我最高能支持OpenFlow 1.0） ---> 交换机55626端口

交换机55626端口（我最高能支持OpenFlow 1.5） ---> 控制器6633端口

于是双方建立连接，并使用OpenFlow 1.0
Features Request
控制器6633端口（我需要你的特征信息） ---> 交换机55626端口
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） ---> 交换机55626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55626端口（这是我的特征信息，请查收） ---> 控制器6633端口
Packet_in
交换机55626端口（有数据包进来，请指示）--- 控制器6633端口
Flow_mod
分析抓取的flow_mod数据包，控制器通过6633端口向交换机55626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55626端口

交互图
交换机与控制器建立通信时是使用TCP协议还是UDP协议？答：TCP

（二）进阶要求
将抓包基础要求第2步的抓包结果对照OpenFlow源码。

Hello

/* 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. */
};
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;
};

Features Request

/* 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. */
};
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;
};

Set Conig

/* 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. */
};

Port Staus

/* 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);

Features Reply

/* 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. */
};
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. */
};

Packet_in

交换机查找流表，没有匹配条目

/* Why is this packet being sent to the controller? */
enum ofp_packet_in_reason {
    OFPR_NO_MATCH,          /* No matching flow. */
    OFPR_ACTION             /* Action explicitly output to controller. */
};

有匹配条目,对应的action是OUTPUT=CONTROLLER,固定收到向控制器发送包

/* 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. */
};

Flow_mod

/* Fields to match against flows */
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. */
};

Packet_out

/* Action header that is common to all actions.  The length includes the
 * header and any padding used to make the action 64-bit aligned.
 * NB: The length of an action *must* always be a multiple of eight. */
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.) */
};

个人总结

抓包时未发现Hello数据包
先开启抓包再构建拓扑
在观察交换机55626端口与控制器6633端口之间的Hello时，过滤出 openflow_v1 中并没看到需要的信息。
过滤器改成openflow_v6就能看到交互情况。
没找到Features Request的源码
查阅资料后发现它与Hello的格式是一致的。
1 . 版本协商在哪个消息类型
Hello
2 . packet_in消息的原因是什么
交换机查找流表，没有匹配条目
有匹配条目,对应的action是OUTPUT=CONTROLLER,固定收到向控制器发送包
3 . packet_out和flow_mod的区别在哪里
mod 控制器向交换机下发流表项，指导数据的转发处理
out 控制器直接告诉交换机该怎么做
通过本次实验，学会了如何运用 wireshark 对 OpenFlow 协议数据交互过程进行抓包；以及借助包解析工具，分析与解释 OpenFlow协议的数据包交互过程与机制。本次实验的总体难度不大，主要是抓包和找源码的时候很费眼睛。

posted @ 2022-09-26 22:59 计科废物3 阅读(120) 评论(0) 收藏举报

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实验3：OpenFlow协议分析实践

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