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How an HSP works with IP filtering


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How an HSP works with IP filtering
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How an HSP works with IP filtering

The Internet connection process with WPS technology for an HSP with IP filtering differs depending on whether the customer attempting to connect is a new customer or an existing customer. The following example describes the process for a new customer. In addition, how IAS handles an expired account is explained.

New customer connection example

When a new customer connects to an HSP and establishes an account with a WISP, the following five basic stages occur:

The customer discovers the HSP network at a Wi-Fi hotspot

The customer authenticates as guest

The client is provisioned with the HSP XML master file

The customer selects a WISP and establishes an account

The customer is authenticated with the new account credentials

In the next section we will look at these stages in more detail.

1.  The customer discovers the HSP network at a Wi-Fi hotspot

When a customer arrives at the HSP hotspot with a portable computer running Windows XP Home Edition with SP2, Windows XP Tablet PC Edition with SP2, or Windows XP Professional with SP2, the computer comes within range of the HSP access point beacon.

The Wireless Auto Configuration service on the client computer detects the beacon information from the access point, which is enabled with broadcast Secure Set Identifier (SSID). The SSID is equivalent to the network name.

The customer is informed by Windows XP that a wireless network is available. The customer views information in Windows XP, and if interested, the customer clicks Connect.

2.  The customer authenticates as guest

Wireless Auto Configuration uses 802.1X and PEAP guest authentication to connect to the HSP network through the access point, automatically passing a null user name and a blank password to the HSP IAS proxy.

The IAS proxy is configured both as a proxy and as an IAS server. The IAS proxy/server is configured to locally process users that authenticate as guest, and to forward other messages to the WISP IAS servers based on the value of the User-Name attribute in the Access-Request message.

The HSP IAS proxy server acts as an IAS server for guest authentication, processing these requests locally rather than acting as a proxy and forwarding them. The HSP IAS proxy server is therefore the PEAP authenticator and TLS endpoint for customers who connect as guest, and the TLS tunnel is created between the client and the HSP IAS server. All subsequent messages between client and server pass through this tunnel.

Server authentication is performed when the HSP IAS server verifies its identity to the client computer using a certificate that contains the Server Authentication purpose in Enhanced Key Usage (EKU) extensions. This certificate is issued by a public trusted root CA.

The HSP IAS proxy server authenticates and authorizes the customer as guest. In the Access-Challenge message that the IAS server sends to the client is a URL PEAP-TLV. The URL PEAP-TLV is a container with a value that is the URL of the HSP provisioning server. This URL provides the client with the location of the HSP XML master file.

The HSP IAS proxy server also sends IP filters in the form of Vendor Specific Attributes (VSAs) to the access point. These IP filters are applied to the client connection by the access point and are used to isolate the client; the filters block access to all network resources except the HSP provisioning server and the WISP provisioning servers.

The customer client computer receives an IP address lease from the HSP DHCP server. The address is from a public IP address range configured in a scope on the DHCP server.

3.  The client is provisioned with the HSP XML master file

The HSP master XML file on the HSP provisioning server contains pointers to multiple WISP master XML files, which in turn contain pointers to each respective WISP’s XML subfiles. Windows XP downloads the HSP XML master file.

Windows displays to the customer a list of WISPs whose services are offered by the HSP.

For this example, the customer selects services from WISP 1.

4.  The customer selects a WISP

After the customer selects the WISP, Windows XP connects to the WISP and, using the Background Intelligent Transfer Service, downloads the WISP XML master file and subfiles. When the XML sign-up schema is downloaded, the sign-up wizard is opened on the client to allow the customer to create and pay for an account with the WISP.

Using the sign-up wizard on the client computer, the customer steps through the process of signing up for an account with WISP 1. The data entered by the customer is converted by Windows XP into an XML document.

The XML document containing the customer’s sign-up data is sent by Windows XP to the Web application on the WISP 1 provisioning server.

The Web application processes the customer payment information. Once payment is verified and sign-up information is completed successfully, the Web application creates a user account in Active Directory, and permissions are applied to the user account by assigning group membership based on the account type chosen by the customer.

An XML document containing the new account credentials is sent from the WISP provisioning server to the client computer. The client computer uses the credentials to configure Wireless Auto Configuration and 802.1X under the name of the WISP.

5.  The customer is authenticated using the new account credentials and gains Internet access

Wireless Auto Configuration restarts the association to the SSID for the HSP.

Wireless Auto Configuration finds the correct 802.11 profile which was downloaded with the other WISP information. Wireless Auto Configuration re-associates using the correct profile.

802.1X restarts the authentication process using PEAP-MS-CHAP v2 and the new account credentials.

As the client starts the authentication process, the HSP IAS proxy forwards messages between the client and the WISP IAS server. The connection request policies on the HSP IAS proxy are configured to forward requests to WISP 1 where the ISP’s name exists in the realm portion of the RADIUS User-Name attribute. For example, if “user@wisp1.example” is the user name, the IAS proxy server uses the realm portion of the user name, “wisp1.example,” to choose the IAS server that should receive the connection request.

In the first stage of PEAP-MS-CHAP v2 authentication, a TLS channel is created between the customer’s client computer and the WISP 1 IAS server.

In the second stage of PEAP-MS-CHAP v2 authentication, the WISP 1 IAS server authenticates and authorizes the connection request against the new account in the user accounts database. The WISP IAS server sends an Access-Accept message that is forwarded by the HSP IAS proxy to the HSP access point.

Because IP filters are used to isolate the client, the IAS server message causes the access server to remove the IP filters from the client connection, granting the customer access to the Internet.

How IAS handles an expired account

Each WISP that offers connectivity through an HSP can determine the types of account plans to offer customers. These plans can range from fees based on hourly use to accounts with lifespans as long as a day, a month, or longer.

It is important for IAS to determine whether a connecting or connected client computer has a valid account, and to take the appropriate action if the customer’s account is expired. The following example illustrates how IAS determines that a twenty-four hour account is current, and how WPS technology behaves when the account expires.

Twenty-four hour connect option example

When the customer arrives at the HSP, the customer chooses an access account with WISP 1 that has a one-day (24-hour) lifespan. The customer and client computer proceed through the account creation process described above, and then connect to the Internet. The following process occurs:

In the Access-Accept message sent by the WISP 1 IAS server, the IAS server sets a session timeout of 60 minutes for the client computer connection to the access point.

After 60 minutes, the access point requests that the client reauthenticate. The client reauthenticates successfully and the customer’s session is not interrupted.

Each 60 minutes thereafter, the access point requests that the client reauthenticate. During each authentication the IAS server checks the current time against the expiry time for the user account to discover whether the customer is authorized to access the network.

On the last re-authentication, at hour 23 in the account lifespan and before 24 hours have passed, the IAS authorization check fails and the IAS server sends a URL PEAP-TLV message to the client that contains the account renewal action parameter and an HTTPS URL for an XML master file. The URL PEAP-TLV supplies the customer with the location of the provisioning server where the customer can renew the account.

Upon receiving the URL in the URL PEAP-TLV, 802.1X requests that Windows XP display the account renewal application to the customer.

The customer renews the account and 802.1X initiates authentication using the account credentials.

During authentication with the WISP 1 IAS server, the IAS server authenticates and authorizes the customer against the user accounts database, and sends an Access-Accept message containing a session timeout of 60 minutes to the access point.

During this process, because the account has not expired, the customer maintains connection to the Internet.

If the customer does not complete the renewal process before the 24 hour account lifespan is reached, then the access point reapplies IP filters and customer access to the Internet is terminated. The customer is then provided with the option of renewing the account for continued access.


This scenario is currently in development and has not been implemented or tested. It is provided as a general depiction of a possible implementation of WPS technology.

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