实验3：OpenFlow协议分析实践
一、实验目的
- 能够运用 wireshark 对 OpenFlow 协议数据交互过程进行抓包；
- 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
Ubuntu 20.04 Desktop amd64
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。
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。
hello
控制器6633端口（我最高能支持OpenFlow 1.0） ---> 交换机40566端口
交换机40566端口（我最高能支持OpenFlow 1.5） ---> 控制器6633端口
Features Request
控制器6633端口（我需要你的特征信息） ---> 交换机40566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40566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40566端口（这是我的特征信息，请查收） ---> 控制器6633端口
PACKET_IN
交换机40566端口（有数据包进来，请指示）--->控制器6633端口
PACKET_OUT
控制器6633端口--->交换机40566端口（请按照我给你的action进行处理）
FLOW_MOD
分析抓取的flow_mod数据包，控制器通过6633端口向交换机40566端口、交换机40566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
4.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？
TCP协议
（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，了解OpenFlow主要消息类型对应的数据结构定义。
1.HELLO
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.OFPT_FEATURES_REQUEST
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;
};
3.OFPT_SET_CONFIG
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.OFPT_PORT_STATUS
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.OFPT_FEATURES_REPLY
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. */
};
6.OFPT_PACKET_IN
有两种情况：
（1）交换机查找流表，发现没有匹配条目，但未发现这种情况。
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
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.OFPT_PACKET_OUT
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.OFPT_FLOW_MOD
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. */
};
四、个人总结
本次实验难度一般，主要是进行抓包的时候需要找仔细一点，我遇到的第一个问题就是在抓包的时候，要先打开抓包的页面再进行拓扑，不然会找不到想要抓包的数据包内容，老师在PPT里面也有强调，主要是我做的时候看得不够认真。还有抓HELLO数据包的时候openflow_v4里找不到数据包，后来通过询问同学发现可以在openflow_v6里面找。还有抓包的时候找交换机端口号相同的数据包，我截图的时候没有注意，后来又重新抓包了一次，浪费了不少时间。
本次实验也让我更加了解如何使用wireshark进行抓包，以及通过抓包到的数据包对其交互过程有了更多的了解与理解，收获满满。