TCP
Format
Flags
| Flag | Name | Description |
|---|---|---|
| CWR | Congestion Window Reduced | 拥塞窗口减小 |
| ECE | ECN-Echo | |
| URG | Urgent | 表示紧急指针字段有效 |
| ACK | Acknowledge | 表示确认字段有效 |
| PSH | Push | 要求将缓冲的数据推送到接收应用程序 |
| RST | Reset | 重置连接 |
| SYN | Synchronize | |
| FIN | Finish | 来自发送方的最后一个数据包 |
Lifecycle
TCP Handshake
TCP Close
TCP Socket Status
| State | Endpoint | Description |
|---|---|---|
| LISTEN | Server | Waiting for a connection request from any remote TCP end-point. |
| SYN-SENT | Client | Waiting for a matching connection request after having sent a connection request. |
| SYN-RECEIVED | Server | Waiting for a confirming connection request acknowledgment after having both received and sent a connection request. |
| ESTABLISHED | Server and client | An open connection, data received can be delivered to the user. The normal state for the data transfer phase of the connection. |
| FIN-WAIT-1 | Server and client | Waiting for a connection termination request from the remote TCP, or an acknowledgment of the connection termination request previously sent. |
| FIN-WAIT-2 | Server and client | Waiting for a connection termination request from the remote TCP. |
| CLOSE-WAIT | Server and client | Waiting for a connection termination request from the local user. |
| CLOSING | Server and client | Waiting for a connection termination request acknowledgment from the remote TCP. |
| LAST-ACK | Server and client | Waiting for an acknowledgment of the connection termination request previously sent to the remote TCP (which includes an acknowledgment of its connection termination request). |
| TIME-WAIT | Server or client | Waiting for enough time to pass to be sure that all remaining packets on the connection have expired. |
| CLOSED | Server and client | No connection state at all. |
QA
TCP最大连接数？
TCP/UDP协议的设计，端口号只有16位，所以只有2^16=65536个端口。 理论上讲，客户端能够建立65535个连接，服务端能建立2^32x2^16=2^48个连接。 实际上，这个数量受以下因素影响：
- 带宽
- 服务器性能
- 最大文件数