curl_exec: Resolving timed out (no replies)

Hello,

I´ve did not find any solution in this forum or the bugtracker for my problem, so I start a new topic.

If I try to install new plugins, I get an error: curl_exec: Resolving timed out after 3153 milliseconds. Hostname requested was: plugins.piwik.org.

If I do a ping from the cli of the server, plugins.piwik.org will get resolved and even the ping responses. If I do a wget http://plugins.piwik.org from cli, this works fine, too.

Has anybody an idea, what my problem could be? We are using Piwik 2.10 on a Centos 7 server with php 5.6

Thanks in advance

Ralf Lutz