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
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
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
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
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;
/* switch configuration. /
struct ofp_switch_config {
uint16_t flags; / ofpc_* flags. /
uint16_t miss_send_len; / max bytes of new flow that datapath should
send to the controller. */
/* a physical port has changed in the datapath /
struct ofp_port_status {
uint8_t reason; / one of ofppr_*. /
uint8_t pad[7]; / align to 64-bits. */
struct ofp_phy_port desc;
struct ofp_switch_features {
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. */
(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 {
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. */
struct ofp_packet_out {
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_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