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The portal server need to know where the where the clientaccess the network, and the information of the cleint, how to achieve it.
Wireless controller can redirect to the portal web with some url-parameter, and the portal server can read it.
You can configure it in the portal web-server. Tips, the param-name can be and string you want if the portal server can read it, but the value of the string can be choosed from the list showed in the picture only.
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portal web-server server-name
rurl-parameter param-name { nas-id | nas-port-id | original-url | source-address | ssid | { ap-mac | source-mac } [ format section { 1 | 3 | 6 } { lowercase | uppercase } ] [ encryption { aes | des } key { cipher | simple } string ] | value expression | vlan }
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