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。
-
搭建拓扑
-
配置相关信息
2.hello
控制器6633端口（我最高能支持OpenFlow 1.0） ---> 交换机38404端口
交换机38404端口（我最高能支持OpenFlow 1.5） ---> 控制器6633端口
3.Features Request / Set Conig
控制器6633端口（我需要你的特征信息） ---> 交换机38404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38404端口
4.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。
5.Features Reply
交换机38404端口（这是我的特征信息，请查收） ---> 控制器6633端口
6.Packet_in
有两种情况：
- 交换机查找流表，发现没有匹配条目时
- 有匹配条目但是对应的action是OUTPUT=CONTROLLER时
交换机38404端口（有数据包进来，请指示）--- 控制器6633端口
7.Packet_out
控制器6633端口（请按照我给你的action进行处理） ---> 交换机38404端口
8.Flow_mod
分析抓取的flow_mod数据包，控制器通过6633端口向交换机38404端口、交换机38404端口下发流表项，指导数据的转发处理
9.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
10.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？
是TCP，可以从报文中直接看出
（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.OpenFlow的数据包头具有通用字段，相关数据结构定义如下：
/* 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. */
};
OFP_ASSERT(sizeof(struct ofp_header) == 8);
2.hello
/* OFPT_HELLO. This message has an empty body, but implementations must
* ignore any data included in the body, to allow for future extensions. */
struct ofp_hello {
struct ofp_header header;
};
3.Features Request
参数源码与hello一致
4. Set Conig
/* 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. */
};
5.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;
};
6.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. */
};
7.Packet_in
(1)交换机查找流表，发现没有匹配条目时
/* Why is this packet being sent to the controller? */
enum ofp_packet_in_reason {
OFPR_NO_MATCH, /* No matching flow. */
OFPR_ACTION /* Action explicitly output to controller. */
};
(2)有匹配条目但是对应的action是OUTPUT=CONTROLLER
/* 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. */
};
8.Packet_out
* Action header that is common to all actions. The length includes the
* header and any padding used to make the action 64-bit aligned.
* NB: The length of an action *must* always be a multiple of eight. */
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];
};
OFP_ASSERT(sizeof(struct ofp_action_header) == 8);
/* 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.) */
};
9.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. */
};
(三）个人总结
1.建立可视化拓扑时，需要改变Preferences中的IP Base为192.168.0.0/24
2.抓包时没有出现hello数据包，应该先开启抓包在运行sudo python 文件.py
3.通过过滤器输入“openflow_v4”时，并没有出现对应的数据包，查询后发现支持的版本是“openflow_v6”，让我对OpenFlow有了更深刻的了解。
4.将抓包结果对照OpenFlow源码，更加了解了OpenFlow主要消息类型对应的数据结构定义。