安卓手机admob广告无法显示的问题

这个问题恶心我好几天,我2个手机,其中的一个可以显示admob广告条,另一个死活出不来,
后来发现android也有host文件控制跳转
如果发现无法显示广告,logcat显示以下错误的话,
查看/system/etc/host文件中是否将googleads.g.doubleclick.net转向了127.0.0.1
将其注释后即可显示广告

logcat info may be shown as follows:

03-07 21:27:43.713: W/Ads(5189): IOException connecting to ad url.
03-07 21:27:43.713: W/Ads(5189): java.net.ConnectException: googleads.g.doubleclick.net/127.0.0.1:80 - Connection refused
03-07 21:27:43.713: W/Ads(5189): at org.apache.harmony.luni.net.PlainSocketImpl.connect(PlainSocketImpl.java:210)
03-07 21:27:43.713: W/Ads(5189): at org.apache.harmony.luni.net.PlainSocketImpl.connect(PlainSocketImpl.java:440)
03-07 21:27:43.713: W/Ads(5189): at java.net.Socket.connect(Socket.java:1013)
03-07 21:27:43.713: W/Ads(5189): at org.apache.harmony.luni.internal.net.www.protocol.http.HttpConnection.<init>(HttpConnection.java:75)
03-07 21:27:43.713: W/Ads(5189): at org.apache.harmony.luni.internal.net.www.protocol.http.HttpConnection.<init>(HttpConnection.java:48)
03-07 21:27:43.713: W/Ads(5189): at org.apache.harmony.luni.internal.net.www.protocol.http.HttpConnection$Address.connect(HttpConnection.java:322)
03-07 21:27:43.713: W/Ads(5189): at org.apache.harmony.luni.internal.net.www.protocol.http.HttpConnectionPool.get(HttpConnectionPool.java:89)
03-07 21:27:43.713: W/Ads(5189): at org.apache.harmony.luni.internal.net.www.protocol.http.HttpURLConnectionImpl.getHttpConnection(HttpURLConnectionImpl.java:285)
03-07 21:27:43.713: W/Ads(5189): at org.apache.harmony.luni.internal.net.www.protocol.http.HttpURLConnectionImpl.makeConnection(HttpURLConnectionImpl.java:267)
03-07 21:27:43.713: W/Ads(5189): at org.apache.harmony.luni.internal.net.www.protocol.http.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:205)
03-07 21:27:43.713: W/Ads(5189): at com.google.ads.b.run(SourceFile:280)
03-07 21:27:43.713: W/Ads(5189): at java.lang.Thread.run(Thread.java:1027)
03-07 21:27:43.733: W/dalvikvm(5189): JNI: DeleteGlobalRef(0xde6f0df7) failed to find entry (valid=0)
03-07 21:27:43.733: W/dalvikvm(5189): JNI: DeleteGlobalRef(0xde6f0dd7) failed to find entry (valid=0)
03-07 21:27:43.733: D/webviewglue(5189): nativeDestroy view: 0x461278
03-07 21:27:43.733: I/Ads(5189): onFailedToReceiveAd(A network error occurred.)