Install logstash-filter-de_dot failed?

I am trying to install logstash-filter-de_dot plugin with below command.
/opt/logstash/bin/plugin install logstash-filter-de_dot

But it shows below error.
Validating logstash-filter-de_dot
Unable to download data from - SocketError: initialize: name or service not known (
ERROR: Installation aborted, verification failed for logstash-filter-de_dot

my logstash version is logstash 2.1.3
What am I missing?

Can you ping from the host? It looks like it's either a general internet accessibility or a DNS issue.

root@hp-dx:~# ping
ping: unknown host

No, ping

ping: unknown host

Can you ping any other host on the internet?

If not then it's a DNS issue.

my dns server setting as follows,

ping yahoo is success