（一）基本要求
1. 导入到/home/用户名/学号/lab3/目录下的拓扑文件
//实践代码如下
#!/usr/bin/env python
from mininet.net import Mininet
from mininet.node import Controller, RemoteController, OVSController
from mininet.node import CPULimitedHost, Host, Node
from mininet.node import OVSKernelSwitch, UserSwitch
from mininet.node import IVSSwitch
from mininet.cli import CLI
from mininet.log import setLogLevel, info
from mininet.link import TCLink, Intf
from subprocess import call
def myNetwork():
net = Mininet( topo=None,
build=False,
ipBase='192.168.0.0/24')
info( '*** Adding controller\n' )
c0=net.addController(name='c0',
controller=Controller,
protocol='tcp',
port=6633)
info( '*** Add switches\n')
s1 = net.addSwitch('s1', cls=OVSKernelSwitch)
s2 = net.addSwitch('s2', cls=OVSKernelSwitch)
info( '*** Add hosts\n')
h1 = net.addHost('h1', cls=Host, ip='192.168.0.101', defaultRoute=None)
h2 = net.addHost('h2', cls=Host, ip='192.168.0.102', defaultRoute=None)
h3 = net.addHost('h3', cls=Host, ip='192.168.0.103', defaultRoute=None)
h4 = net.addHost('h4', cls=Host, ip='192.168.0.104', defaultRoute=None)
info( '*** Add links\n')
net.addLink(h1, s1)
net.addLink(h3, s1)
net.addLink(s1, s2)
net.addLink(s2, h2)
net.addLink(s2, h4)
info( '*** Starting network\n')
net.build()
info( '*** Starting controllers\n')
for controller in net.controllers:
controller.start()
info( '*** Starting switches\n')
net.get('s1').start([c0])
net.get('s2').start([c0])
info( '*** Post configure switches and hosts\n')
CLI(net)
net.stop()
if __name__ == '__main__':
setLogLevel( 'info' )
myNetwork()
2. Wireshark抓包结果
-
OFPT_HELLO 控制器6633端口（我最高能支持OpenFlow 1.0） ---> 交换机38928端口
-
-
交换机38928端口（我最高能支持OpenFlow 1.5） ---> 控制器6633端口
控制器与交换机建立连接，并使用OpenFlow 1.0
-
OFPT_FEATURES_REQUEST 控制器6633端口（我需要你的特征信息） ---> 交换机38928端口
控制器请求交换器的特征信息
-
OFPT_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38928端口
控制器要求交换机按照所给出的信息进行配置
-
OFPT_PORT_STATUS 源端口38928 -> 目的端口6633，从交换机到控制器
当交换机端口发生变化时，告知控制器相应的端口状态。
-
OFPT_FEATURES_REPLY 交换机38928端口（这是我的特征信息，请查收） ---> 控制器6633端口
交换机告知控制器它的特征信息
-
OFPT_PACKET_IN 交换机38928端口（有数据包进来，请指示）--->控制器6633端口
交换机告知控制器有数据包进来，请求控制器指示
-
OFPT_PACKET_OUT 控制器6633端口--->交换机38928端口（请按照我给你的action进行处理）
控制器要求交换机按照所给出的action进行处理
-
OFPT_FLOW_MOD 分析抓取的flow_mod数据包，控制器通过6633端口向交换机38928端口、交换机38932端口下发流表项，指导数据的转发处理
-
3.画出相关交互图或流程图：
7.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。
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;
};
可以看到对应了HELLO报文的四个参数
2. FEATURES_REQUEST
源码参数格式与HELLO相同，与上述ofp_header结构体中数据相同
3.SET_CONFIG
控制器下发的交换机配置数据结构体
/* 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. */
};
可以看到与图中信息一一对应，包括交换机物理端口的信息
6. PACKET_IN
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
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_header99 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];
};
（三）实验总结
-
本次实验较简单，主要是使用wireshark进行抓包以及对抓包结果进行分析制作流程图
-
运行wireshark后，运行拓扑结构后，未在抓包列表中找到OFPT_FLOW_MOD类型，多次重复无果后，尝试输入pingall得到想要的结果
-
在进行抓包时必须一次性完成所有包的查找分析，否则再次启动虚拟机时，会发生两次抓包同一个包而端口不一致的情况
-
通过本次实验，我能够熟练地运用 wireshark 对 OpenFlow 协议数据交互过程进行抓包，学会在过滤器输入 "openflow_v1" 或 "openflow_v6" 对数据包进行过滤，对 OpenFlow 协议的数据包交互过程与机制有了更深入的了解。