实验3:OpenFlow协议分析实践
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 20.04 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 |
- 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?
(1)HELLO
控制器6633端口(我最高能支持OpenFlow 1.0) ---> 交换机52108端口
交换机52126端口(我最高能支持OpenFlow 1.5) ---> 控制器6633端口
于是双方建立连接,并使用OpenFlow 1.0
(2)FEATURES_REQUEST
从控制器6633端口到交换机57126端口,请求特征信息。
(3)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57126端口
(4)FEATURES_REPLY
交换机57126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52128端口(有数据包进来,请指示)--- 控制器6633端口
(6)FLOW_MOD
分析抓取的flow_mod数据包,控制器通过6633端口向交换机57126端口下发流表项,指导数据的转发处理
(7)PACKET_OUT
控制器6633端口(请按照我给你的action进行处理) ---> 交换机57126端口
使用TCP协议,如图所示可以看出,拓扑文件中也有写出是使用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。
(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. */
};
(2)FEATURES_REQUEST
源码与OFPT_HELLO代码一致(因为ofp_header为所有报文的头)
(3)OFPT_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)OFPT_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. */
};
(5)OFPT_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. */
};
(6)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.) */
};
(7)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
- 实验过程一开始无法打开wireshark后,仔细看pdf后知道要使用命令sudo wireshark开启。
- 通过先启动wireshark,再执行python文件,然后执行pingall命令,才能捕获到HELLO数据包。
- 学会了通过滤器输入“openflow_v1”或“openflow_v4”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;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,让我们能够了解OpenFlow主要消息类型对应的数据结构定义
- 本次实验操作难度并不大,主要时间都花费在寻找各种数据包上面
- 更加熟练地使用wireshark抓包工具。同时,也利用抓包结果与openflow源码对照学习,了解了openflow主要消息类型对应的数据结构定义