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。
-
hello
- 控制器6633端口（我最高能支持OpenFlow 1.0） ---> 交换机60026端口
- 交换机60026端口（我最高能支持OpenFlow 1.5） ---> 控制器6633端口
- Features Request：控制器6633端口（我需要你的特征信息） ---> 交换机60026端口
- Set Conig：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60026端口
- Port_Status：当交换机端口发生变化时，告知控制器相应的端口状态
- Features Reply：交换机60026端口（这是我的特征信息，请查收） ---> 控制器6633端口
- Packet_in
- Packet_out
- Flow_mod：分析抓取的flow_mod数据包，控制器通过6633端口向交换机60026端口、交换机60028端口下发流表项，指导数据的转发处理
- 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？
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。
0、openflow数据包头通用格式
/* 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. */
};
1、OFPT_HELLO
/* OFPT_HELLO. This message has an empty body, but implementations must
* ignore any data included in the body, to allow for future extensions. */
struct ofp_hello {
struct ofp_header header;
};
2、OFPT FEATURES REQUEST
struct ofp_stats_request {
struct ofp_header header;
uint16_t type; /* One of the OFPST_* constants. */
uint16_t flags; /* OFPSF_REQ_* flags (none yet defined). */
uint8_t body[0]; /* Body of the request. */
};
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、OFPT_FEATURES REPLY
struct ofp_stats_reply {
struct ofp_header header;
uint16_t type; /* One of the OFPST_* constants. */
uint16_t flags; /* OFPSF_REPLY_* flags. */
uint8_t body[0]; /* Body of the reply. */
};
/* Body of reply to OFPST_AGGREGATE request. */
struct ofp_aggregate_stats_reply {
uint64_t packet_count; /* Number of packets in flows. */
uint64_t byte_count; /* Number of bytes in flows. */
uint32_t flow_count; /* Number of flows. */
uint8_t pad[4]; /* Align to 64 bits. */
};
OFP_ASSERT(sizeof(struct ofp_aggregate_stats_reply) == 24);
/* Body of reply to OFPST_TABLE request. */
/* Queue configuration for a given port. */
struct ofp_queue_get_config_reply {
struct ofp_header header;
uint16_t port;
uint8_t pad[6];
struct ofp_packet_queue queues[0]; /* List of configured queues. */
};
OFP_ASSERT(sizeof(struct ofp_queue_get_config_reply) == 16);
/* OFPAT_ENQUEUE action struct: send packets to given queue on port. */
6、Packet_In
/* Why is this packet being sent to the controller? */
enum ofp_packet_in_reason {
OFPR_NO_MATCH, /* No matching flow. */
OFPR_ACTION /* Action explicitly output to controller. */
};
/* 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. */
};
OFP_ASSERT(sizeof(struct ofp_packet_in) == 20);
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. */
};
/* Modify behavior of the physical port */
struct ofp_port_mod {
struct ofp_header header;
uint16_t port_no;
uint8_t hw_addr[OFP_ETH_ALEN]; /* The hardware address is not
configurable. This is used to
sanity-check the request, so it must
be the same as returned in an
ofp_phy_port struct. */
uint32_t config; /* Bitmap of OFPPC_* flags. */
uint32_t mask; /* Bitmap of OFPPC_* flags to be changed. */
uint32_t advertise; /* Bitmap of "ofp_port_features"s. Zero all
bits to prevent any action taking place. */
uint8_t pad[4]; /* Pad to 64-bits. */
};
OFP_ASSERT(sizeof(struct ofp_port_mod) == 32);
8、Packet_Out
/* Action structure for OFPAT_OUTPUT, which sends packets out 'port'.
* When the 'port' is the OFPP_CONTROLLER, 'max_len' indicates the max
* number of bytes to send. A 'max_len' of zero means no bytes of the
* packet should be sent.*/
struct ofp_action_output {
uint16_t type; /* OFPAT_OUTPUT. */
uint16_t len; /* Length is 8. */
uint16_t port; /* Output port. */
uint16_t max_len; /* Max length to send to controller. */
};
OFP_ASSERT(sizeof(struct ofp_action_output) == 8);
/* 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.) */
};
OFP_ASSERT(sizeof(struct ofp_packet_out) == 16);
（三）个人总结
实验难度：
本次实验的难度不是特别大，是验证性的实验,只要实验步骤正确，一般是可以得到正确的结果的。主要困难在于理解 OpenFlow 协议的数据包交互过程，以及 openflow 头文件各种数据包结构。
实验过程遇到的困难及解决办法：
一开始一直抓不到 OpenFlow 包，后来又一直不知道怎么找到 FLOW_MOD 包；后面按照指导书一步步又走过一遍，就解决了问题。
个人感想：
通过本次实验的学习，学习了如何在 WireShark 中利用过滤器抓取指定的数据包。同时在抓包结果与openflow头文件源码对照学习中，对openflow主要消息类型对应的数据结构定义，以及penFlow协议的数据包交互过程与机制有了更加深入的了解。