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
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。
进行相关IP配置
2.命令行拓扑完整性测试
3.查看抓包结果
HELLO
控制器6633端口到交换机36642端口（使用OpenFlow 1.0协议)
从控制器36642端口到交换机6633端口（使用OpenFlow1.5协议）
OFPT_HELLO后，双方协商使用openflow1.0协议
FEATURES_REQUEST
从控制器6633端口到交换机36642端口，请求特征信息
SET_CONFIG
控制器6633端口到交换机36642端口
PORT_STATUS
从交换机36642端口到控制器6633端口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36642端口到控制器6633端口，回复特征信息
PACKET_IN
交换机36642端口到控制器6633端口（有数据包进来，请指示）
PACKET_OUT
控制器6633端口到交换机36642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36642端口、交换机36642端口下发流表项，指导数据的转发处理
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？
如图所示为（Transmission Control Protocol）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。
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. */
};
2.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. */
};
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
/* 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. */
};
6.PACKET_IN
有两种情况：
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
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. */
};
个人总结
遇到的问题
- 实验过程中执行python文件后，打开wireshark后进行抓包，用openflow_v1过滤时，并没有发现HELLO数据包，后来发现要先进行wireshark之后，再执行python文件，就可以发现HELLO数据包了。
- 运行拓扑结构后，再运行wireshark后并未在抓包列表中找到MOD类型，找了很多次发现并没有，后来尝试输入pingall后在抓包列表里找到了该数据包。
实验心得
- 这次实验总体来说不是很难，就是需要认真和耐心，在抓包时要格外细心，因为数据包不太好找。
实验收获
- 这次实验学会用过滤器输入“OpenFlow_v1和Openflow_v6”等进行数据包过滤，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，将抓包结果对照OpenFlow源码，了解到OpenFlow主要消息类型对应的数据结构定义。
