I have an interesting behavior. When my guest users attach to the guest network, I want them to use some external DNS source and not my organizations DNS servers. So, I set the dhcp scope options to point to other DNS Servers. When I do, the users don't seem to be redirected to the WLC guest portal, they get nothing and because of that, they cannot get to the Internet.
I am not sure why this is happening. The re-direction URL is https://1.1.1.1/login.html?redirect=www.google.com?/ocid=iehp
I don't understand why pointing a guest client to an external DNS servers would cause the guest login page not to come up.
The issue is likely that you are attempting to redirect an HTTPS page. See this link for more information:
http://www.cisco.com/c/en/us/support/docs/wireless-mobility/wlan-security/115951-web-auth-wlc-guide-00.html#anc7
You didn't mention your code rev, but it seems that 8.0 is able to redirect HTTPS for guest portal.
doublepost