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
3.1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。
主机 | IP地址 |
---|---|
h1 | 192.168.0.101/24 |
h2 | 192.168.0.102/24 |
h3 | 192.168.0.103/24 |
h4 | 192.168.0.104/24 |
- 在miniedit中构建好后存为topo.py,并在代码中更改主机IP地址
- 命令行搭建拓扑ping检测是否正确
3.2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。
-
Hello
- 控制器6633端口(我最高能支持OpenFlow 1.0)---> 交换机55570端口
- 交换机55570端口(我最高能支持OpenFlow 1.5) ---> 控制器6633端口
- 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; };
- 控制器6633端口(我最高能支持OpenFlow 1.0)---> 交换机55570端口
-
Features Request/Set Conig
- 控制器6633端口(我需要你的特征信息) ---> 交换机55570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55570端口
- 源码
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. */ };
- 控制器6633端口(我需要你的特征信息) ---> 交换机55570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
-
源码
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; };
-
-
Features Reply
- 交换机44026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. */ }; 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. */ };
- 交换机44026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55570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
- 源码
enum ofp_packet_in_reason { OFPR_NO_MATCH, /* No matching flow. */ OFPR_ACTION /* Action explicitly output to 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. */ };
- 前者是没成功匹配的,后者是收到向控制器发送的包
- 有两种情况:
-
Flow_mod
- 分析抓取的flow_mod数据包,控制器通过6633端口向交换机44026端口、交换机44028端口下发流表项,指导数据的转发处理
- 源码
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. */ }; 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. */ };
- 分析抓取的flow_mod数据包,控制器通过6633端口向交换机44026端口、交换机44028端口下发流表项,指导数据的转发处理
-
Packet_out
- 控制器6633端口(请按照我给你的action进行处理) ---> 交换机44026端口
- 告诉输出到交换机的65531端口
- 源码
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]; }; 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.) */ };
- 控制器6633端口(请按照我给你的action进行处理) ---> 交换机44026端口
-
流程图
3.3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:在使用wireshark抓包时,可以清楚看到是使用TCP协议。
总结
遇到问题及解决方法:
- 在筛选交换机向控制器传的Hello参数时,没能找到,直到筛选openflow_v6才成功找到。
- 找不到flow_mod参数,在将任意两主机ping通后再重新抓包,成功找到。
个人感想
这次实验难度对我来说中等。大部分的环节是抓包、筛选、看代码,由于在前几次实验中对大部分相关的实验步骤都熟悉了许多,这次实验做起来比较迅速。遇到的错误也能很快得到解决。最麻烦的一点其实是去openflow.h看源代码,不过也能运用一些类如word的工具来快速查找。最大的收获是对openflow协议的数据交互更加清晰,对wireshark的运用也更加熟练了。