实验3：OpenFlow协议分析实践
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
- 下载虚拟机软件Oracle VisualBox；
- 在虚拟机中安装Ubuntu 20.04 Desktop amd64，并完整安装Mininet；
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包。
- 导入拓扑文件
2.wireshark抓包结果
-
控制器6633端口（我最高能支持OpenFlow 1.0）-->交换机52522端口
-
交换机52522端口（我最高支持OpenFlow 1.5）-->控制器6633端口
-
控制器6633端口（我需要你的特征信息）--> 交换机52526端口
-
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52526端口
-
当交换机端口发生变化时，告知控制器相应的端口状态
- 回答：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。
-
Features Reply
- 交换机52522端口（这是我的特征信息，请查收）-- 控制器6633端口
- 交换机52522端口（这是我的特征信息，请查收）-- 控制器6633端口
-
源码
-
/* 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. */
};
OFP_ASSERT(sizeof(struct ofp_phy_port) == 48);
/* Switch features. */
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. */
};
- Packet_in
- 交换机52522端口（有数据包进来，请指示）--控制器6633端口
- 交换机52522端口（有数据包进来，请指示）--控制器6633端口
-源码
/* 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. */
};
- Flow_mod
- 控制器通过6633端口向交换机54408端口、交换机54386端口下发流表项、指导数据的转发处理
- 控制器通过6633端口向交换机54408端口、交换机54386端口下发流表项、指导数据的转发处理
- 源码
/* Fields to match against flows */
struct ofp_match {
uint32_t wildcards; /* Wildcard fields. */
uint16_t in_port; /* Input switch port. */
uint8_t dl_src[OFP_ETH_ALEN]; /* Ethernet source address. */
uint8_t dl_dst[OFP_ETH_ALEN]; /* Ethernet destination address. */
uint16_t dl_vlan; /* Input VLAN id. */
uint8_t dl_vlan_pcp; /* Input VLAN priority. */
uint8_t pad1[1]; /* Align to 64-bits */
uint16_t dl_type; /* Ethernet frame type. */
uint8_t nw_tos; /* IP ToS (actually DSCP field, 6 bits). */
uint8_t nw_proto; /* IP protocol or lower 8 bits of
* ARP opcode. */
uint8_t pad2[2]; /* Align to 64-bits */
uint32_t nw_src; /* IP source address. */
uint32_t nw_dst; /* IP destination address. */
uint16_t tp_src; /* TCP/UDP source port. */
uint16_t tp_dst; /* TCP/UDP destination port. */
};
/* 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. */
};
- Packet_out
- 控制器6633端口（请按照我给你的action进行处理）-->交换机54408端口
- 控制器6633端口（请按照我给你的action进行处理）-->交换机54408端口
- 源码
/* Action header that is common to all actions. The length includes the
* header and any padding used to make the action 64-bit aligned.
* NB: The length of an action *must* always be a multiple of eight. */
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];
};
OFP_ASSERT(sizeof(struct ofp_action_header) == 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.) */
};
（三）个人总结
- 这次实验通过wireshark抓包让我对OpenFlow协议的数据包交互过程与机制更加熟悉了，实验过程中也遇到许多问题，比如运行拓扑的时候忘记先打开wireshark抓包了，结束拓扑再运行却看不到hello等消息，最后是把整个终端关闭重新再运行才能看到；还有样例中是OpenFlow 1.3，但是实际上是OpenFlow 1.5，所以最后选择openflow_v6才看到，之前没想到要换成v6，一直找不到。查找源代码时，源码都在openflow.h文件中，可以通过右上角save旁边的三条杠的按钮，里面有find功能，十分方便。这次实验难度适中，困难之处主要是要去理解这些数据的信息，深入了解OpenFLow协议。总而言之，这次实验我收获匪浅。
