Take the 2-minute tour ×
Unix & Linux Stack Exchange is a question and answer site for users of Linux, FreeBSD and other Un*x-like operating systems.. It's 100% free, no registration required.

I'm running Arch Linux on my netbook. My school have an open Access Point and we must sign into the network via a page which we are redirected to when we try to open whatever website if we are not connected.

It works on my Android Smartphone. It works on Windows. It should also works on Linux since my teacher is able to connect to it (he's running Ubuntu).

I connect to the access point with wifi-menu to generate a netctl profile. I am connected but I am not redirected to the login page, and when I type the address (taken from my phone) it don't find the server... I tried disabling IPv6, but nothing change...

share|improve this question
    
It's running a service like networkmanager on your system? –  mavillan Sep 6 '13 at 6:47
    
I don't think so... I have netctl which use wpa_supplicant... I discovered that there's also another network, which is securised by WPA. I can put login using my credentials that I should put in the login page for the open network, but I still can't access the web... Tried with my phone : it works... –  Shywim Sep 6 '13 at 7:28
    
It sounds like this could be an DNS issue. Can you confirm if you can access a remote host directly via an IP address? –  Thomas Nyman Sep 6 '13 at 19:14

1 Answer 1

up vote 3 down vote accepted

What you describe is called a captive portal. They are typically used for authentication on Wi-Fi hotspots, but can be used to control wired network access as well.

There are several ways to implement a captive portal:

  • HTTP Redirection

    In this case, DNS queries from unauthenticated clients are resolved as normal. However, when the browser makes a HTTP request to the resolved IP address, the request is intercepted by a firewall acting as a transparent proxy. The client HTTP request is forwarded to a server in the local network which issues a server-side redirect with a HTTP 302 Found status code, which will redirect the client to the captive portal.

  • DNS Redirection

    In DNS based redirection the firewall ensures that only the DNS server(s) provided by DHCP may be used by authenticated clients. The firewall could also redirect any DNS queries from unauthenticated clients to the local DNS server. This DNS server will in turn return the IP address of the captive portal as a response to all DNS lookups made by unauthenticated clients.

  • IP Redirection

    In redirection working on the IP layer a router performs Destination Network Address Translation (DNAT) to reroute packets originating from an captive hosts to the captive portal. In cases where the captive portal software runs on the router itself, the packets are directed to an internal interface instead. Packets headed from the captive portal to the host get in turn their source address rewritten so that they would appear to originate from the original destination.

When troubleshooting captive portal issues, the first step would be to identify what type of redirection is in use and at which point the redirection fails. The right tool for this job is a packet analyzer, such as Wireshark. Keep in mind though, that your school's IT policy might prohibit the use of packet sniffers on the local network as such tools could easily be used to invade the privacy of others on an unencrypted network.

You could also consult the tech support at your school. They would be aware of the captive portal configuration on the local Wi-Fi network, and especially if faculty members are using Linux they probably could help in pinpointing the source of the problem.

share|improve this answer
    
@Shywim My post is not much of an answer, but it's hard to give specific advice without knowing more about the specific captive portal solution used at your school. –  Thomas Nyman Sep 6 '13 at 19:02
    
That's fine, it is very instructive. My problem seems to be different (I have the same problem with other networks), but I'll leave this question and accept your answer. :) –  Shywim Sep 9 '13 at 9:43
    
I would find it useful if this answer were edited to include information about what to look for in the packet traffic and how to respond accordingly. –  inquiryqueue Dec 11 at 19:11

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.