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Thread: Zero Config Internet access for a captive portal IP conflict issue

  1. #1

    Zero Config Internet access for a captive portal IP conflict issue

    Dear all,

    I've been working on this project for some time now... and hit a dead end...! so some guidance and ideas would be much appreciated.

    The Project:

    Its to do with providing internet access to computers who have configured their IP addresses using static settings. The objective is not to change any settings on the guest computers. This is to work as an add-on for a captive portal. Normally to get internet access the guests have to drop their static settings and set them selves to DHCP. for example this is useful in a Hotel ... guests will have static settings configured .. and they would access the internet via captive portal with out changing to DHCP. I am basicaly;

    1. Listening for multiple unanswered ARP requests on the network
    2. Once its been verified that a guest with static IP settings is looking for a non-existent gateway, the gateway IP is created on a computer(sever) as an aliased IP through which the guest will now have internet access.
    3. The server is a standard pc with 2 bridged NIC's (NATed) running Ubuntu 10 something

    my problem:

    When there are 2 guests with the same IP there is an IP conflict! and i have no way of granting them internet access.

    Possible solution?
    wouldn't isolating the clients using private VLAN or AP isolation be a solution?

    Your comments are most welcome,

    Thanks in Advance!

  2. #2
    redhead's Avatar
    Join Date
    Jun 2001
    Copenhagen, Denmark
    If you can't change any settings on the clients, there's no way of preventing matching IPs.
    In a situation where two machines have the same IP, you could route their interenetaccess through a squid proxy, telling them "your IP has a match, please change it" else theres not much you can do.

    If you want to isolate them, you can say the DHCP will hand out IPs from 192.168/32 and their static IPs must be within 172.16/8 else I dont see how you want them to be seperate, when the clients can't be changed.
    Don't worry Ma'am. We're university students, - We know what We're doing.
    'Ruiat coelum, fiat voluntas tua.'
    Datalogi - en livsstil; Intet liv, ingen stil.

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