> For the complete documentation index, see [llms.txt](https://jon-xia.gitbook.io/workspace/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://jon-xia.gitbook.io/workspace/gong-cheng-4/ji-suan-ji-wang-luo/tcp/tcp-gai-nian.md).

# tcp概念

三次握手：

```sql
        **LISTENING**
        A --> SYN=1 B
SYN_SENT
        A SYN=1 ACK-1 <-- B
                            SYN_RCVD
        A --> ACK=1 B

        **ESTABLISHED**
```

四次挥手：

```sql
        **ESTABLISHED**
        A --> FIN=1 B
FIN_WAIT_1
        A ACK=1 <-- B
FIN_WAIT_2                  CLOSE_WAIT
        A FIN=1 ACK=1  <-- B
TIME_WAIT                   LAST_ACK
        A --> ACK=1 B
        **CLOSED**
```