Why does portal authentication not automatically pop up the Web page?

Why does portal authentication not automatically pop up the Web page? (Manual redirection can succeed and go online normally.)

1.      Generally speaking, if the DNS server is reachable, it can be automatically redirected. Check whether the DNS configuration is correct, and allow the DNS address in the portal free-rule.

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[AC] portal free-rule 1 destination ip any udp 53

[AC] portal free-rule 2 destination ip any tcp 53

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2.      The reason why Portal-authenticated page clients can automatically pop up is that when the terminal is connected to Wi-Fi, the terminal system will automatically send an HTTP request to a page (for example, the IOS terminal will send an HTTP request to several fixed web sites of IOS). Then the device configured with portal authentication will intercept it, and then force the portal authentication interface to be pushed out. Some terminals cannot actively pop up the interface because these terminals will not automatically send an HTTP request to a certain page after connecting to Wi-Fi. In this case, the customer needs to manually send an HTTP request in the browser.