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。
-
搭建拓扑
-
配置相关信息
- 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。
- OFPT_HELLO
从 6633 端口到 59502 端口，OpenFlow 1.0 协议
从 59488 端口到 6633 端口，OpenFlow 1.5 协议
- OFPT_FEATURES_REQUEST
从 6633 端口到 59488 端口，OpenFlow 1.0 协议
- OFPT_SET_CONFIG
从 6633 端口到 59488 端口，OpenFlow 1.0 协议
- OFPT_PORT_STATUS
从 59502 端口到 6633 端口，OpenFlow 1.0 协议
- OFPT_FEATURES_REPLY
从 59488 端口到 6633 端口，OpenFlow 1.0 协议
- OFPT_PACKET_IN
从 59488 端口到 6633 端口，OpenFlow 1.0 协议
- OFPT_PACKET_OUT
从 6633 端口到 59488 端口，OpenFlow 1.0 协议
- OFPT_FLOW_MOD
从 6633 端口到 59488 端口，OpenFlow 1.0 协议
- 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？
答：TCP协议，见下图（Transmission Control Protocol）：
（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。
- OFPT_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;
};
- OFPT_FEATURES_REQUEST
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;
};
- OFPT_SET_CONFIG
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. */
};
- OFPT_PORT_STATUS
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;
};
- OFPT_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. */
};
- OFPT_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. */
};
- OFPT_PACKET_OUT
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.) */
};
- OFPT_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. */
};
四、个人总结
-
实验心得：本次实验总体来说比较简单，复习了创建、运行拓扑的操作流程；进一步熟悉使用wireshark抓包工具；解了OpenFlow协议中交换机与控制器的消息交互过程；通过查看OpenFlow源码，了解了OpenFlow几个主要消息类型对应的数据结构定义。
-
实验过程遇到的问题及解决方法
- 抓包时找不到数据包；
解决方法：先开启抓包再运行拓扑。 - 运行拓扑时使用
sudo mn --custom mysdntopo3.py --topo mytopo --mac命令，提示错误；
解决方法：改用sudo python mysdntopo3.py。
- 抓包时找不到数据包；