There is a captive portal login page that must be signed before I get internet access, and that page is not opening because I don't have internet. When I try to open it via the URL, it says "DNS_PROBE_FINISHED_NO_INTERNET" on Chrome and something similar on other browsers.

Important points:

  • My Wifi adapter is Realtek RTL8723DE

  • It works fine on all other Wifi networks than my school network

  • All my other devices work fine on the school network and the captive portal opens

  • I used to be able to connect to the internet on the school network on my PC earlier as well, I can't think of any hardware or software change on my part that has triggered this issue.

  • My school network is protected by WPA2, and I have the password and can connect to the Wifi network without issues, but it says "No Internet".

What I've already tried:

  • Restarting my pc

  • Making sure my Wifi drivers are up to date

  • Opening an http:// site without ssl, still says no internet

  • Opening the captive portal URL(I know it) on many different browsers.

  • Getting in touch with the school network admin, not helpful

  • Do you have any VPN software installed? Do you use custom (static) DNS server addresses? Can you get any result out of nslookup superuser.com or nslookup <captive_portal_domain>?
    – user1686
    Jul 12 '19 at 11:37
  • 1
    You would probably do better to request assistance from your school's IT support people. Jul 12 '19 at 11:42
  • No vpn. I seem to be using google DNS. the result of nslookup <captiveportal> is DNS request timed out. timeout was 2 seconds. Server: UnKnown Address: DNS request timed out. timeout was 2 seconds. DNS request timed out. timeout was 2 seconds. DNS request timed out. timeout was 2 seconds. DNS request timed out. timeout was 2 seconds. *** Request to UnKnown timed-out @grawity
    – Enne
    Jul 12 '19 at 11:43
  • Switch to DHCP-provided DNS servers, then try again.
    – user1686
    Jul 12 '19 at 11:49
  • 1
    I was going to comment you have internet but your DNS was wrong hence the DNS error :$
    – Ramhound
    Jul 12 '19 at 12:32

As it was determined in comments, the problem is (almost always) caused by custom DNS server addresses being configured on the PC, instead of using DHCP-provided ones.

When captive portals block access to the Internet, they block everything, DNS included. (Aside from being the default result, it also avoids bypassing the portal through DNS tunneling.)

Sometimes the captive portal will intercept outbound DNS queries and redirect them all to its local DNS server, but many portals don't do that and simply drop those packets along with the rest.

So when trying to log into a captive-portal network, you really should be using DHCP-provided local DNS servers (even if you think they don't work well) – using as your DNS server often simply won't work at all.

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