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
- 下载虚拟机软件Oracle VisualBox；
- 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
· 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。
· 所创建拓扑结构中有两个交换机，以其中端口号为35242的交换机为例。
Hello
· 控制器6633端口（我最高能支持OpenFlow 1.0） ---> 交换机35242端口
· 交换机35242端口（我最高能支持OpenFlow 1.3）--- 控制器6633端口
· OpenFlow协议向下兼容，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35242端口
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35242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35242端口（这是我的特征信息，请查收）--- 控制器6633端口
Packet_IN:
Packet_Out:
Flow_Mod:
· 分析抓取的flow_mod数据包，控制器通过6633端口向交换机35242端口、交换机35264端口下发流表项，指导数据的转发处理
· 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。
· 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？
通过wireshark抓包工具，可一看出使用的是TCP协议（Transmission Control Protocol）。
（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。
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;
};
Features_Request:
· Features_Request消息类型的格式与Hello一致，含有一个头部ofp_header。
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. */
};
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;
};
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:
PACKET_IN有两种情况：
· 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. */
};
· 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. */
};
OFP_ASSERT(sizeof(struct ofp_packet_in) == 20)
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.) */
};
OFP_ASSERT(sizeof(struct ofp_packet_out) == 16);
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];
};
（三）实验报告
⚪ 实验难度：适中
· 本次实验在于利用wireshark抓包工具，获取OpenFlow协议数据包，然后分析各种数据包的用途，分析控制器与交换机的交互关系。进阶实验通过查看源码，验证自己所抓取的数据包。
⚪ 实验过程遇到的困难：
· 问题1：打开wireshark后创建拓扑，过滤Openflow数据包，并未找到Flow_Mod数据包
解决：阅读文档，Flow_Mod数据包是控制器想交换机下发流表项，指导数据的转发处理，于是启动wireshark后尝试执行pingall，找到了Flow_mod数据包。
· 问题2：保存wireshark抓包文件后，再用wireshark打开.pcapng文件，权限不足。
解决：输入命令行"sudo chmod 777 xxx.pcapng"解决此问题，777代表，user,group ,others ,都有读写和可执行权限。
⚪ 收获与感想：
· 收获：能够熟悉运用 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；对拓扑建立使用到的协议和数据交互流程有了更深的理解；更加熟悉了mininet的一些命令行操作；。
· 感想：本次实验难度不大，通过wireshark抓取数据包、抓取数据包学习了OpenFlow协议下控制器和交换机的交互过程，涉及到多个不同用途的数据包，分析这些数据包的版本、类型、源端口、目的端口和相关字段。截图、源码很多，整理实验报告，画流程图很花实践，但再过程中可以加深对控制器与交换机交互过程的理解。实验任有疏漏，还需要继续补缺！。。。
