I have a Laptop with debian jessie installed. At my home network, i could connect successfully to the internet (
ping google.de successful). At the external network, i can't ping google.de (result: unknown host google.de), although i can ping 18.104.22.168 and 22.214.171.124 (those are the google public dns servers Source)
/etc/resolv.conf was configured to use a private DNS resolver(nameserver 255.0.0.0) at home, therefore it doesn't work at the external network. Changing that to nameserver 126.96.36.199 and 188.8.131.52 as suggested in 1 doesn't help, it is overwritten after the dhclient is run. chmod -w /etc/resolv.conf (it has now only read permissions) also doesn't help. It is still overwritten, when running dhclient.
I use ifup and ifdown and those legacy tools to connect.
iface wlan0 inet dhcp
Now my question:
You need to make sure DHCP (if in use) is configured correctly, and your local DHCP server (usually your cable / adsl modem) is handing out the right details.
How do i do that? I can't use that suggestion, because obviously i have no internet connection.