實驗任務一
試驗任務二
OpenFlow協議中交換機與控制器的消息交互過程如下圖所示
Hello
首先，控制器與交互及互相發送 Hello 消息。
Features Request
其次，OpenFlow 連接建立之后,控制器需要獲得交換機的特性信息，因此控制器向交換機發送 Features Request 消息查詢交換機特性.
Features Reply
交換機在收到控制器發出的 Features Request 消息后，將自己的特性告訴給控制器，返回 Features Request 消息.
Set config
知道了交換機的特性之后就要配置交換機了。
Packet-in
有兩種情況會觸發交換機向控制器發送 Packet_in 消息
- 1.數據包在交換機中匹配不到流表，則向controller發送Packet_in消息
- 2.數據包在流表中有匹配的條目，但是其中所指示的 action 列表中包含轉發給控制器的動作（Output = CONTROLLER）
(注：該圖是因為匹配不到流表，屬於第一種)
Flow-Mod / Packet-out
當控制器收到 Packet-in 消息時有兩種響應的方式:
- Flow-Mod：控制器收到 Packet‐in 消息后，可以發送 Flow‐Mod 消息向交換機下發一個流表項。
- Packet-out：與Flow-Mod不同的是，控制器不會下發流表，而是直接告訴交換機該如何做。
（Flow-Mod）
（Packet_out）
實驗任務三
Q:交換機與控制器建立通信時是使用TCP協議還是UDP協議？TCP協議
進階任務
OFPT_Hello
Hello包定義了一個header，header數據結構如下：
struct ofp_header {
uint8_t version; /* 版本號 */
uint8_t type; /* Openflow 協議類型. */
uint16_t length; /* Openflow 數據包包頭. */
uint32_t xid; /* 數據包編號. */
};
struct ofp_hello {
struct ofp_header header;
};
OFPT_ERROR
如果連接失敗，會發送一個error包,error類型如下。
enum ofp_error_type {
OFPET_HELLO_FAILED, /* Hello protocol failed. */
OFPET_BAD_REQUEST, /* Request was not understood. */
OFPET_BAD_ACTION, /* Error in action description. */
OFPET_FLOW_MOD_FAILED, /* Problem modifying flow entry. */
OFPET_PORT_MOD_FAILED, /* Port mod request failed. */
OFPET_QUEUE_OP_FAILED /* Queue operation failed. */
};
OFPT_FEATURES
OFPT_FEATURES 主要是請求交換機的特性，而交換機的特性數據結構定義如下
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
OFPT_PACKET_IN產生的原因有兩種，一種是沒匹配到流表，另一種是匹配到了，動作是轉發的控制器，代碼如下
enum ofp_packet_in_reason {
OFPR_NO_MATCH, /* No matching flow. */
OFPR_ACTION /* Action explicitly output to controller. */
};
OFPT_PACKET_IN的數據格式如下：
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
packet_in事件之后，一般會觸發兩類事件，packet_out和flow_mod。兩者都是指導交換機如何處理數據包，區別是是否下發流表項。packet_out數據結構如下。
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
Flow-Mod：控制器收到 Packet‐in 消息后，可以發送 Flow‐Mod 消息向交換機下發一個流表項。指導交換機轉發數據包，其數據格式如下：
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. */
};
OFP_ASSERT(sizeof(struct ofp_flow_mod) == 72);
/* Why was this flow removed? */
enum ofp_flow_removed_reason {
OFPRR_IDLE_TIMEOUT, /* Flow idle time exceeded idle_timeout. */
OFPRR_HARD_TIMEOUT, /* Time exceeded hard_timeout. */
OFPRR_DELETE /* Evicted by a DELETE flow mod. */
};
個人心得
源碼閱讀其實有很多內容可寫，如果把整個流程寫出來，就太麻煩了。所以這邊就非常簡單寫了一些OpenFlow主要消息類型對應的數據結構定義。還有交互過程也應該詳細一些的。不過不太符合作業簡要的要求，就沒寫太多。