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

• 导出的拓扑文件存入目录：/home/用户名/学号/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。

HELLO

控制器6633端口（我最高能支持OpenFlow 1.0） <--> 交换机44936端口

FEATURES_REQUEST

控制器端口6633 --> 交换机端口44936

SET_CONFIG

控制器端口6633 --> 交换机端口44936

PORT_STATUS

交换机端口49032 --> 控制器端口44936

FEATURES_REPLY

交换机端口49032 --> 控制器端口44936

PACKET_IN

交换机端口49032 --> 控制器端口44936

PACKET_OUT

控制器端口6633 --> 交换机端口44936

FLOW_MOD

控制器端口6633 --> 交换机端口44936

• 画出相关交互图或流程图
  

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：TCP协议

（二）进阶要求

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

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

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. */
};

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;
};

5. 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. /
};
/ 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

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

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

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];
};

四、个人总结

• 本次实验基础原理难度不大，就是对于协议数据报的抓包和分析，简单地构建网络拓补结构后开启抓包软件便可以开始数据包传递流向的分析，直观的还原了网络报文握手交互的全过程。实验过程中的操作基本在PDF的文件指导下可以比较顺利地完成下来。关于进阶要求，将数据报文分类对照OpenFlow码源的数据定义结构后，对于各报文的类型定义和实现功能与过程有了更进一步的体会。再来就是实验报告的攥写，本次实验过程截图内容要求比较多，关于相关控制器、交换机端口需要仔细查找，由于抓包软件筛选之后的数据报文内容过多，需要逐条去比对筛查，截图保存，整个过程时间耗费比较长，需要比较耐心的整理，不过稳定执行相关步骤后还是能较好的完成。