Unable to add packages

[Karel Lucas]

Hi all,
Entered on a fresh install of openBSD : pkg_add bash. I got the 
following error: ftp: ftp.nluug.nl/pub/OpenBSD: no address associated 
with name. Not too long ago I did this on another machine and it worked. 
The correct site is listed in /etc/installurl: 
https://ftp.nluug.nl/pub/OpenBSD. Can someone give me a tip on how to 
solve this?