TIME_WAIT state

[lang_zh]
在寫計網作業時，發現只要有 client 連進來，在 httpd 砍掉之後，沒辦法馬上再 bind 同一個 port。netstat 看到了 TIME_WAIT。

Active close 一個 connection 時，必須在 TIME_WAIT state 等待 2 x MSL (/maximum segment lifetime/) 的時間。RFC 1122 的建議值是 120 秒。但是 Linux 的實作上 follow BSD，把 MSL 設為 30 秒，net/ipv4/tcp_minisocks.c 裡面有這段註解:
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[lang_en]
When I wrote my Computer Network's homework, I found that binding to the same port will be failed after a client comes in and stop the httpd. I see TIME_WAIT state when execute netstat.

One should wait in TIME_WAIT state for 2 x MSL (/maximum segment lifetime/) after close one connection. The suggestion time interval in RFC 1122 is 120 seconds. But the implementation of Linux follows BSD, which set MSL to 30 seconds. There's a comment in net/ipv4/tcp_minisocks.c:
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* [ BTW Linux. following BSD, violates this requirement waiting
*   only for 60sec, we should wait at least for 240 secs.
*   Well, 240 consumes too much of resources 8)
* ]

[lang_zh]
試了一下時間，真的是一分鐘 Q_Q 本來是在做測試，懶得把 port 寫在參數裡面。看來得辛苦一點點啦 XD

BTW, Unix Network Programming 真是好書呀!!

Update:
用 setsockopt 打開 SO_REUSEADDR 可以解決這個問題
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[lang_en]
I observed the time, and it really about 1 minute Q_Q So I should add a port to the argument :/

BTW, Unix Network Programming is really a great book!

Update:
Use setsockopt to enable SO_REUSEADDR will solve this problem.
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