hymond
11
Basically, DNSmasq (the DNS and DHCP service on OpenWRT) prevents DNS responses from the upstream DNS server (usually provided by DHCP) that fall in any of the common private IP address spaces. Unticking the option allows those responses through. I’d recommend not generally leaving that unchecked since it does provide a measure of protection against possible spoofing vulnerabilities. Setting the DNS servers to something public like OpenDNS doesn’t alleviate the issue since generally the authentication service/site happens within the private address space of wherever the captive portal lives.
What you can do if you happen to know the DNS suffix of whatever the captive portal uses is to configure that domain in the whitelist further down on the page. It’ll allow those private address responses from those domains only, and not globally. Its a good solution if you stick to a particular hotel chain and can’t be bothered to toggle the global setting on and off every time.
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