实验3：OpenFlow协议分析实践
实验3：OpenFlow协议分析实践
（一）基本要求
拓扑文件
2-1. 查看抓包结果
-
Hello
控制器6633端口（我最高能支持OpenFlow 1.0） ---> 交换机51726端口
交换机51726端口（我最高能支持OpenFlow 1.5） ---> 控制器6633端口
于是双方建立连接，并使用OpenFlow 1.0 -
Features_Request
控制器6633端口（我需要你的特征信息） ---> 交换机51726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51726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51726端口（这是我的特征信息，请查收） ---> 控制器6633端口
Packet_In
•有两种情况：
•交换机查找流表，发现没有匹配条目时
•有匹配条目但是对应的action是OUTPUT=CONTROLLER时
交换机51726端口（有数据包进来，请指示）--->控制器6633端口
分析抓取的数据包，可以发现是因为交换机发现此时自己并没有匹配的流表（Reason:
No matching flow (table-miss flow entry) (0)），所以要问控制器如何处理
Packet_Out
控制器6633端口--->交换机51726端口（请按照我给你的action进行处理）
告诉输出到交换机的51726端口
Flow_Mod
分析抓取的flow_mod数据包，控制器通过6633端口向交换机51726端口、交换机51732端口下发流表项，指导数据的转发处理
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
交换机与控制器建立通信时是使用TCP协议还是UDP协议？
使用的是TCP协议
（二）进阶要求
OpenFlow的数据包头具有通用字段，相关数据结构定义如下
hello
源码：
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;
};
features_reply
源码：
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. */
};
set_config
源码：
/* 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. */
};
post_status
源码：
/* 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;
};
packet_in
源码：（有匹配条目但是对应的action是OUTPUT=CONTROLLER时）
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. */
};
源码：（交换机查找流表，发现没有匹配条目时）
enum ofp_packet_in_reason {
OFPR_NO_MATCH, /* No matching flow. */
OFPR_ACTION /* Action explicitly output to controller. */
};
packet_out
源码：
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.) */
};
flow_mod
源码：
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];
};
个人总结
1.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，当然细心还是很重要的。
2.在实验过程中我遇到的困难并不多，就是刚开始的时候没抓到flow_mod的数据包，后来经过反复地尝试，将拓扑运行，主机通信等一系列过程都进行抓包，很快就找到 flow_mod的数据包。还有后来在画交互图时稍微卡了一下，因为不知道各种包的发送顺序，经过反复对抓取的数据包的分析，以及上网查找资料，最终画出了一张个人觉得正确的交互图。
3.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。
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；将抓包结果对照OpenFlow源码，让我们能够了解OpenFlow主要消息类型对应的数据结构定义。
