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 22.04.1 LTS Desktop amd64
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。
| 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 |
拓扑文件Python代码截图如下
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。
1.hello
控制器6633端口（我最高支持OpenFlow1.0）--->交换机52188端口
交换机52188端口（我最高支持OpenFlow1.5）--->控制器6633端口
2.Features Request/Set Config
控制器6633端口（我需要你的特征信息） ---> 交换机52188端口
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52188端口
3.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。
4.Features Reply
交换机52188端口（这是我的特征信息，请查收） ---> 控制器6633端口
5.packet_in
交换机52188端口（有数据包进来，请指示）--- 控制器6633端口
6.Packet_out
控制器6633端口（请按照我给你的action进行处理） ---> 交换机52188端口
7.flow_mod
分析抓取的flow_mod数据包，控制器通过6633端口向交换机52188端口下发流表项，指导数据的转发处理
8.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
由图可知采用的是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. */
};
struct ofp_hello {
struct ofp_header header;
};
2.FEATURE 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. */
};
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. */
};
//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 Switch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.FEATURE_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
四、个人总结
本次实验的难度总体不大，主要是让我们熟悉wireshark的使用及OpenFlow的源码。在完成基本要求的过程中，我遇到了如下问题：在开启wireshark抓包后，使用mininet中pingall指令，发现抓到的openflow包中没有OFPT_HELLO，我通过参考实验指导PDF和网络上查找到的相关资料，先运行wireshark开始抓包，然后再构建拓扑。重新试验之后，我得到了完整的openflow抓包信息。之后的实验过程都很顺利，实验结果也符合预期。
进阶要求完成得很顺利，在路径openflow/include/openflow中找到openflow.h，打开查找，第2步中相对应的结构体仔细些都能找到。在查看Open Flow源码并与抓包结果进行比对的过程中，我了解了openflow主要消息类型对应的数据结构定义，更加了解了交换机和控制器建立连接的步骤以及详细过程。