实验3：OpenFlow协议分析实践
（一）基本要求
-
拓扑文件
-
wireshark抓包的结果
OFPT_HELLO
控制器6633端口（我最高能支持OpenFlow 1.0） ---> 交换机55692端口
交换机55692端口（我最高能支持OpenFlow 1.5） ---> 控制器6633端口
控制器与交换机建立连接，并使用OpenFlow 1.0
OFPT_FEATURES_REQUEST 控制器6633端口（我需要你的特征信息） ---> 交换机55692端口
控制器请求交换器的特征信息
OFPT_SET_CONFIG 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55692端口
控制器要求交换机按照所给出的信息进行配置
OFPT_PORT_STATUS 源端口55692 -> 目的端口6633，从交换机到控制器
当交换机端口发生变化时，告知控制器相应的端口状态。
OFPT_FEATURES_REPLY 交换机55692端口（这是我的特征信息，请查收） ---> 控制器6633端口
交换机告知控制器它的特征信息
OFPT_PACKET_IN 交换机55692端口（有数据包进来，请指示）--->控制器6633端口
交换机告知控制器有数据包进来，请求控制器指示
OFPT_PACKET_OUT 控制器6633端口--->交换机55692端口（请按照我给你的action进行处理）
控制器要求交换机按照所给出的action进行处理
OFPT_FLOW_MOD 分析抓取的flow_mod数据包，控制器通过6633端口向交换55692端口、交换机55692端口下发流表项，指导数据的转发处理
3.画出相关交互图或流程图：
交换机与控制器建立通信时是使用TCP协议还是UDP协议？
使用的是TCP协议
（二）进阶要求
1.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. */
};
//HELLO报文中有四个参数，对应版本号、消息类型、长度及ID
struct ofp_hello {
struct ofp_header header;
};
2.FEATURES_REQUEST
feature_request的结构与hello一致
/* 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. */
};
//feature_request的结构与hello一致
3.SET_CONFIG
/* 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. */
};
//set_config比header还多了两项
//flags:交换机如何处理IP分片数据包
//miss_send_len:一个交换机无法处理的数据包到达时，将数据包发给控制器的最大字节数
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;
};
//在OpenFlow交换机中添加、删除或修改物理端口时，需要发送Port-Status 消息来通知OpenFlow 控制器
5.FEATURES_REPLY
/* 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. */
};
//除了header还包括唯一ID号、缓冲区可以缓存的最大数据包个数、流表数量、功能、动作、端口等
6.PACKET_IN
//两种情况：1.交换机查找流表，发现没有匹配条目,但是这种包没有抓到过
enum ofp_packet_in_reason {
OFPR_NO_MATCH, /* No matching flow. */
OFPR_ACTION /* Action explicitly output to controller. */
};
// 2.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. */
};
7.PACKET_OUT
/* 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.) */
};
//包括动作列表、缓冲区ID等
8.FLOW_MOD
/* 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. */
};
//包括流表项标志符cookie，command代表五种操作，对应值分别为0-4，优先级等
三、个人总结
1.本次实验难度比较低，按照pdf文档一步步做便可完成，但是我一开始没有在数据抓包里找到HELLO，通过多次的尝试后发现是要先打开wireshark，然后选择any后再打开topo并抓包，再运行032002103.py，在这步上花费了比较多的时间。
2.hello：双方选取Hello消息中最低版本的协议作为通信协议如果有一方不支持Openflow协议版本，应发送Error消息后断开连接。如果双方Openflow版本可以兼容，则Openflow连接建立成功。
3.OpenFlow交换机把传统网络中完全由交换机/路由器控制的报文转换为由交换机和控制器共同完成的数据转发操作，实现了数据转发与路由控制的分离。
通过对抓包结果和 OpenFlow 源码的比较，了解了 OpenFlow 主要消息类型对应的数据结构定义。
