实验3:OpenFlow协议分析实践
(一)基本要求
1./home/用户名/学号/lab3/目录下的拓扑文件
2.wireshark抓包的结果截图和对应的文字说明
- hello
控制器6633端口(我最高能支持OpenFlow 1.0) ---> 交换机59728端口
交换机59728端口(我最高能支持OpenFlow 1.0) ---> 控制器6633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59728端口
- Features Request
控制器6633端口(我需要你的特征信息) ---> 交换机59728端口
- Features Reply
交换机59728端口(这是我的特征信息,请查收) ---> 控制器6633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。
- Packet_in
• 有两种情况:
•交换机查找流表,发现没有匹配条目时
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
• 有匹配条目但是对应的action是OUTPUT=CONTROLLER时
交换机59728端口(有数据包进来,请指示)--- 控制器6633端口
- Packet_out
控制器6633端口(请按照我给你的action进行处理) ---> 交换机59728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33640端口下发流表项,指导数据的转发处理
3.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
4.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
(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。 - hello
/* Header on all OpenFlow packets. */
struct ofp_header {
uint8_t version; //版本号 /* OFP_VERSION. */
uint8_t type; //消息类型 /* One of the OFPT_ constants. */
uint16_t length; //长度 /* Length including this ofp_header. */
uint32_t xid; //id /* Transaction id associated with this packet.
Replies use the same id as was in the request
to facilitate pairing. */
};
OFP_ASSERT(sizeof(struct ofp_header) == 8);
/* 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;
};
- Set Conig
enum ofp_config_flags {
/* Handling of IP fragments. */
OFPC_FRAG_NORMAL = 0, /* No special handling for fragments. */
OFPC_FRAG_DROP = 1, /* Drop fragments. */
OFPC_FRAG_REASM = 2, /* Reassemble (only if OFPC_IP_REASM set). */
OFPC_FRAG_MASK = 3
};
//flag不同的值代表不同的处理方式
/* Switch configuration. */
struct ofp_switch_config {
struct ofp_header header;
uint16_t flags; //用来指示交换机如何处理 IP 分片数据包 /* OFPC_* flags. */
uint16_t miss_send_len; //用来指示当一个交换机无法处理的数据包到达时,将数据包发给控制器的最大字节数。 /* Max bytes of new flow that datapath should
send to the controller. */
};
OFP_ASSERT(sizeof(struct ofp_switch_config) == 12);
- Features Reply
/* Switch features. */
struct ofp_switch_features {
struct ofp_header header;
uint64_t datapath_id; //唯一标识ID号/* Datapath unique ID. The lower 48-bits are for
a MAC address, while the upper 16-bits are
implementer-defined. */
uint32_t n_buffers; //缓冲区可缓存的最大数据包个数 /* Max packets buffered at once. */
uint8_t n_tables; //流表数量/* Number of tables supported by datapath. */
uint8_t pad[3]; /* Align to 64-bits. */
/* Features. */
uint32_t capabilities; //支持的特殊功能 /* Bitmap of support "ofp_capabilities". */
uint32_t actions; //支持的动作 /* Bitmap of supported "ofp_action_type"s. */
/* Port info.*/
struct ofp_phy_port ports[0]; //物理端口描述列表 /* Port definitions. The number of ports
is inferred from the length field in
the header. */
};
OFP_ASSERT(sizeof(struct ofp_switch_features) == 32);
- 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. */
};
//该参数与hello报文结构相同
- 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;
};
OFP_ASSERT(sizeof(struct ofp_port_status) == 64);
//这个是当交换机端口发生变化时,告知控制器相应的端口状态
//发生变化包括增加、删除、修改物理端口,则需发送port status来告知
- 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. */
};
//第一行是没有匹配的条目,第二行是action列表中包含转发给控制器的动作。
//两种情况:1.交换机查找流表,发现没有匹配条目,但是这种包没有抓到过2.有匹配条目,对应的action是OUTPUT=CONTROLLER,固定收到向控制器发送包(分别是这上下两段代码)
/* Packet received on port (datapath -> controller). */
struct ofp_packet_in {
struct ofp_header header;
uint32_t buffer_id; //Packet-in消息所携带的数据包在交换机缓存区中的ID /* ID assigned by datapath. */
uint16_t total_len; //data字段的长度 /* Full length of frame. */
uint16_t in_port; //数据包进入交换机时的端口号 /* Port on which frame was received. */
uint8_t reason; //发送Packet-in消息的原因 /* Reason packet is being sent (one of OFPR_*) */
uint8_t pad;
uint8_t data[0]; //携带的数据包 /* 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);
- Packet_out
/* Send packet (controller -> datapath). */
struct ofp_packet_out {
struct ofp_header header;
uint32_t buffer_id; //交换机缓存区id,如果为-1则指定的为packet-out消息携带的data字段 /* ID assigned by datapath (-1 if none). */
uint16_t in_port; //如果buffer_id为‐1,并且action列表中指定了Output=TABLE的动作,in_port将作为data段数据包的额外匹配信息进行流表查询
/* Packet's input port (OFPP_NONE if none). */
uint16_t actions_len; //action列表的长度,可以用来区分actions和data段 /* Size of action array in bytes. */
struct ofp_action_header actions[0]; //动作列表 /* Actions. */
/* uint8_t data[0]; */ // 数据缓存区,可以存储一个以太网帧,可选 /* 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);
- Flow_mod
/* Flow setup and teardown (controller -> datapath). */
struct ofp_flow_mod {
struct ofp_header header;
struct ofp_match match; //流表的匹配域 /* Fields to match */
uint64_t cookie; // 流表项标识符 /* Opaque controller-issued identifier. */
/* Flow actions. */
uint16_t command; //可以是ADD,DELETE,DELETE-STRICT,MODIFY,MODIFY-STRICT /* One of OFPFC_*. */
uint16_t idle_timeout; //空闲超时时间 /* Idle time before discarding (seconds). */
uint16_t hard_timeout; //最大生存时间 /* Max time before discarding (seconds). */
uint16_t priority; //优先级,优先级高的流表项优先匹配 /* Priority level of flow entry. */
uint32_t buffer_id; //缓存区ID ,用于指定缓存区中的一个数据包按这个消息的action列表处理 /* Buffered packet to apply to (or -1).
Not meaningful for OFPFC_DELETE*. */
uint16_t out_port; //如果这条消息是用于删除流表则需要提供额外的匹配参数 /* 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; //标志位,可以用来指示流表删除后是否发送flow‐removed消息,添加流表时是否检查流表重复项,添加的流表项是否为应急流表项。 /* One of OFPFF_*. */
struct ofp_action_header actions[0]; //action列表/* The action length is inferred
from the length field in the
header. */
};
OFP_ASSERT(sizeof(struct ofp_flow_mod) == 72);
(三)个人总结
- 一定要先开启抓包再构建拓扑,不然wireshark抓包抓不到hello包
- 通过抓包了解openflow协议中交换机与控制器的消息交互过程与机制
- 不懂的记得到网络上去了解相关的信息,与同学多沟通自己遇到的问题,别一个人死磕
- 进阶通过抓包和openflow源码相对照可了解主要的消息类型的结构定义