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

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

1.下载虚拟机软件Oracle VisualBox；
2.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。

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

1.IP配置

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.

1).OFPT_HELLO 源端口6633 -> 目的端口47708，从控制器到交换机,此处协议为openflow1.0

2).源端口47708 -> 目的端口6633的，即交换机到控制器的另一个包，此处协议为openflow1.5

3).OFPT_FEATURES_REQUEST 源端口6633 -> 目的端口47708，从控制器到交换机. (控制器请求交换器的特征信息)

4).OFPT_SET_CONFIG 源端口6633 -> 目的端口47708，从控制器到交换机. (控制器要求交换机按照所给出的信息进行配置)

5).OFPT_PORT_STATUS 源端口47708 -> 目的端口6633，从交换机到控制器. (当交换机端口发生变化时，交换机告知控制器相应的端口状态)

6).OFPT_FEATURES_REPLY 源端口47708 -> 目的端口6633，从交换机到控制器. (交换机告知控制器它的特征信息)

7).OFPT_PACKET_IN 源端口47708 -> 目的端口6633，从交换机到控制器. (交换机告知控制器有数据包进来，请求控制器指示)

8).OFPT_PACKET_OUT 源端口6633 -> 目的端口47708，从控制器到交换机. (控制器要求交换机按照所给出的action进行处理)

9).OFPT_FLOW_MOD 源端口6633 -> 目的端口47708，从控制器到交换机. (控制器对交换机进行流表的添加、删除、变更等操作)

3.画出相关交互图。

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？
TCP协议

（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。相关数据结构可在openflow安装目录openflow/include/openflow当中的openflow.h头文件中查询到

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. */
};
struct ofp_hello {
struct ofp_header header;
};

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

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. /
};
/ 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. */
  };

6.PACKET_IN (有两种情况)

(1).交换机查找流表，发现没有匹配条目

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. /
};
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];
};

四.实验总结

这次的实验难度较低，主要是让我们熟悉运用 wireshark 对 OpenFlow 协议数据交互过程进行抓包。
抓包的过程中，唯一难点在于找到想要抓包的那行数据，而 FEATURES_REPLY 和 PACKET_IN 中间所隔较远，即使在过滤器的帮助下依然隔了五百行数据。
这次在保存python文件后，为了方便修改ip，用的依然是将只读文件改成可读可改文件的方法，不知道其他人用的是什么方法直接修改代码