一个用户端最多和同一http server 并发多少TCP连接？

2008年07月30日 14954点热度 0人点赞 4条评论

之前看资料，有多次看到过说客户端在与一个服务器之间（特指http 服务）最多建立2个TCP连接来传输http request。F5可以利用express connect通过增加域名的方式来增加连接数。

我观察过多次，访问我的www.mycisco.cn 总能看到10个连接
TCP 192.168.0.185:3632    125.76.229.121:80    ESTABLISHED
TCP 192.168.0.185:3633    125.76.229.121:80    ESTABLISHED
TCP 192.168.0.185:3634    125.76.229.121:80    ESTABLISHED
TCP 192.168.0.185:3635    125.76.229.121:80    ESTABLISHED
TCP 192.168.0.185:3636    125.76.229.121:80    ESTABLISHED
TCP 192.168.0.185:3637    125.76.229.121:80    ESTABLISHED
TCP 192.168.0.185:3638    203.171.232.42:80    ESTABLISHED
TCP 192.168.0.185:3639    125.76.229.121:80    ESTABLISHED
TCP 192.168.0.185:3640    125.76.229.121:80    ESTABLISHED
TCP 192.168.0.185:3641    125.76.229.121:80    ESTABLISHED
TCP 192.168.0.185:3642    125.76.229.121:80    ESTABLISHED

这就让我迷惑。今天在网上一番google，终于明白了点：
原来根据RF2616的要求，客户端和同一个server之间确实只能建立不超过2个TCP（http 1.1是2个，1.0是4个连接）连接以避免拥塞
Clients that use persistent connections SHOULD limit the number of simultaneous connections that they maintain to a given server. A single-user client SHOULD NOT maintain more than 2 connections with any server or proxy. A proxy SHOULD use up to 2*N connections to another server or proxy, where N is the number of simultaneously active users. These guidelines are intended to improve HTTP response times and avoid congestion.

但是这个不是绝对的，不同的浏览器行为可能并不一样。对于IE有这样一个注册表设置：
MaxConnectionsPerServer REG_DWORD (Default 2)
Sets the number of simultaneous requests to a single HTTP 1.1 Server

MaxConnectionsPer1_0Server REG_DWORD (Default 4)
Sets the number of simultaneous requests to a single HTTP 1.0 Server

这是标准的，但是我的电脑是IE7，他们的值都是10
我查了微软的文档，http://support.microsoft.com/kb/183110/en-us，6.0（含）以前的版本应该都是2. 大家可以验证下。

我将限制值改为2后，再查看发现确实只能同时建立2个TCP连接了。
  Proto  Local Address       Foreign Address       State
  TCP 0.0.0.0:135          0.0.0.0:0             LISTENING
  TCP 0.0.0.0:443          0.0.0.0:0             LISTENING
  TCP 0.0.0.0:445          0.0.0.0:0             LISTENING
  TCP 0.0.0.0:2869          0.0.0.0:0             LISTENING
  TCP 0.0.0.0:15000       0.0.0.0:0             LISTENING
  TCP 127.0.0.1:1045       0.0.0.0:0             LISTENING
  TCP 127.0.0.1:1100       0.0.0.0:0             LISTENING
  TCP 127.0.0.1:62514       0.0.0.0:0             LISTENING
  TCP 192.168.0.185:139    0.0.0.0:0             LISTENING
  TCP 192.168.0.185:1071    219.133.60.243:8000 CLOSE_WAIT
  TCP 192.168.0.185:2307    121.0.19.146:16000    ESTABLISHED
  TCP 192.168.0.185:3609    60.28.183.195:80    TIME_WAIT
  TCP 192.168.0.185:3615    60.28.183.195:80    TIME_WAIT
  TCP 192.168.0.185:3618    125.76.229.121:80    ESTABLISHED
  TCP 192.168.0.185:3619    125.76.229.121:80    ESTABLISHED
  TCP 192.168.0.185:3620    203.171.232.42:80    ESTABLISHED
  TCP 192.168.0.185:3621    125.46.105.130:80    ESTABLISHED
  TCP 192.168.0.185:3623    60.12.231.25:80       ESTABLISHED
  TCP 192.168.0.185:3624    60.12.231.15:80       ESTABLISHED
  TCP 192.168.0.185:3625    61.189.20.200:80    SYN_SENT
  TCP 192.168.0.185:4952    207.46.107.64:1863    ESTABLISHED
  TCP 192.168.0.185:4989    207.46.26.130:1863    ESTABLISHED
  TCP 192.168.0.185:4990    64.4.36.22:1863       ESTABLISHED
  TCP 192.168.0.185:4991    207.46.26.76:1863    ESTABLISHED
  TCP 192.168.0.185:4992    65.54.171.33:1863    ESTABLISHED
  TCP 192.168.0.185:4993    65.54.171.39:1863    ESTABLISHED
  TCP 192.168.0.185:4995    207.46.26.153:1863    ESTABLISHED
  TCP 192.168.124.1:139    0.0.0.0:0             LISTENING
  TCP 192.168.194.1:139    0.0.0.0:0             LISTENING