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How a WISP works using IP filters


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How a WISP works using IP filters

The Internet connection process with WPS technology for a WISP 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 a WISP and establishes an account, the following four basic stages occur:

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

The customer authenticates as guest

The client is provisioned and the customer establishes an account

The customer is authenticated with the new account credentials

IP filters are removed and the customer gains access to the Internet

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

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

When a customer arrives at the WISP Wi-Fi hotspot with a portable computer running Windows XP Home Edition with SP1, Windows XP Professional with SP1, or Windows XP Tablet PC Edition with SP1, the computer comes within range of the WISP 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 WISP network through the access point, automatically passing a null user name and a blank password to the WISP IAS server.

The IAS server is the PEAP authenticator and TLS endpoint for customers who connect as guest, and the TLS tunnel is created between the client and the IAS server. All subsequent messages between client and server pass through this tunnel.

Server authentication is performed when the 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 certification authority (CA).

The IAS 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 provisioning server. This URL provides the client with the location of the XML master file.

The IAS 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 WISP provisioning server.

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

3.  The client is provisioned and the customer creates an account

The XML master file on the provisioning server contains pointers to the XML subfiles. Windows XP downloads the XML master file and subfiles. When the XML sign-up schema is downloaded, the sign-up wizard is launched 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. The data entered by the customer is converted by Windows XP into an XML document.

The XML document containing the customerís sign-up data is sent by Windows XP to the Web application on the WISP 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.

4.  The customer is authenticated with the new account credentials

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

Wireless Auto Configuration finds the correct 802.11 profile which was downloaded with the other WISP information. Wireless Auto Configuration re-associates with the access point 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 with PEAP-MS-CHAP v2 authentication, a TLS channel is created between the customerís client computer and the WISP IAS server.

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

5.  IP filters are removed and the customer gains access to the Internet

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

You can determine the types of account plans that you want to offer your customers. These plans can range from fees based on hourly use to accounts with life spans 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 customerís 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 WISP, the customer chooses an access account 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 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 customerís 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 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 with the account credentials.

During authentication with the 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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