Am Sonntag 29 Oktober 2017 schrieb deloptes:
> Stefan Krusche wrote:
> > $ �ping mirror.xcer.cz
> > PING mirror.xcer.cz (91.241.23.210) 56(84) bytes of data.
> > From 10.2.252.114 icmp_seq=2 Destination Host Unreachable
> >
> > Here from Berlin, Germany. However, "10.2.252.114" looks suspicious to
> > me, because netrange �10.0.0.0 - 10.255.255.255 is a private address
> > usually used by internal networks of big company IIUC, i.e. my provider.
> > When I ping the Freie Universit�t Berlin, I get this:
>
> 10.2.252.114 must be your address from which the ping is executed

Thank you. I would have exspected that to be the individual IP address of my 
computer, because I executed it on my system. I guess it has been changed 
through the networks of my internet provider.

Anyways, it is now clear that the problem addressed by the OP was that 
mirror.xcer.cz was actually down. Understanding the internals of ping is beyond 
the horizon of my expertise.

Regards, Stefan