实验3：OpenFlow协议分析实践

一、基础要求

（一）导入到/home/用户名/学号/lab3/目录下的拓扑文件

（二）wireshark抓包的结果截图和对应的文字说明

（1）HELLO

控制器6633端口（OpenFlow 1.0） ---> 交换机52436端口

交换机52436端口（OpenFlow 1.5） ---> 控制器6633端口

（2）Features Request / Set Conig

控制器6633端口 ---> 交换机52436端口

控制器6633端口 ---> 交换机52436端口

（3）Port_Status

（4）Features Reply

（5）Packet_in

（6）Flow_mod

（7）Packet_out

（三）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

（四）交换机与控制器建立通信时是使用TCP协议还是UDP协议？

TCP

二、进阶要求

（一）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;
};

(二)Features Request / Set Conig

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. */
};

（三）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;
};

（四）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. */
};

（五）Packet_in

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. */
};

（六）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];
};

（七）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.) */
};

三、个人感想

本次实验的步骤简单，具体只分为两步，但是要想领悟背后的逻辑，对我来说依旧存在一定困难。
一是在packet in pack out 阶段，与其他同学相比，所处数列较大，有一点困惑。
二是在对实验复盘中发现无法找到post status，让我很是困惑。
三是在进阶要求中，要对OpenFlow源码，阅读过程中知识盲点较多，需要不断查阅资料，是本次实验中比较困难的部分。
通过本次实验，我学到了运用 wireshark 对 OpenFlow 协议数据交互过程进行抓包以及通过对照OpenFlow源码对OpenFlow主要消息类型对应的数据结构有了初步了解。