linux机器上的squid代理客户端设置

在linux机器中设置squid代理客户机的正确设置是什么？我按照文档设置导出变量，如下所示

bash $ export http_proxy="http://10.20.5.48:3128"   
bash $ ping google.com
PING google.com (74.125.228.197) 56(84) bytes of data.
^C
--- google.com ping statistics ---
1 packets transmitted, 0 received, 100% packet loss, time 922ms

bash $ export http_proxy="http://10.20.5.48:3128/" 
bash $ ping google.com
PING google.com (173.194.123.110) 56(84) bytes of data.

bash $ export HTTP_PROXY="http://10.20.5.48:3128"
bash $ ping google.com                           
PING google.com (74.125.228.196) 56(84) bytes of data.
^C
--- google.com ping statistics ---
2 packets transmitted, 0 received, 100% packet loss, time 1086ms

bash $ export HTTP_PROXY="http://10.20.5.48:3128/"
bash $ ping google.com                            
PING google.com (74.125.228.195) 56(84) bytes of data.
^C
--- google.com ping statistics ---
2 packets transmitted, 0 received, 100% packet loss, time 1160ms

squid服务器在端口3128上运行，可以访问，squid.conf也没有防火墙或acl问题

bash $ telnet 10.20.5.48 3128
Trying 10.20.5.48...
Connected to 10.20.5.48.
Escape character is '^]'.

当我将yum.conf更改为使用具有相同服务器和IP的代理时，yum配置工作将不使用http代理。 尝试

GET/HTTP/1.1
主持人：google.com

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