DNS error while there is in fact no problem with the connection

For a couple of months I get an error going to Saleforce: error dns_probe_finished_nxdomain. It seems like there is no internet connection, but in fact my connection is fine. Other browsers will give the same error. Sometimes it is the main site, sometimes only our Sandbox cannot be reached. There is one colleague with the same problem, but not at the same time. Usually the site will be available again in about 10 minutes. We both encounter this when we work at home, so far not at the office. So it seems to be some local settings. Restarting laptop and modem don't help, using a different laptop gives the same error. Any help to solve this problem would be appreciated, as happens several times per day. (Sorry if this isn't the right tag for this kind of problem, if it isn't can you help me to get it right?) #Trailhead Challenges