Assigning IP Addresses Based on APN

Steel-Belted Radius Carrier can assign IP addresses to mobile devices based on the access point name (APN).

Overview

APN-based IP address assignment enables Steel-Belted Radius Carrier to perform the task of address assignment, rather than requiring the access point to assign addresses.

This feature works by configuring IP address pools, each of which consists of a set of IP addresses that can be assigned to a mobile device. You then configure an access point name (APN) to be associated with a particular pool. When an Access-Request is received, Steel-Belted Radius Carrier selects an IP address from the pool that is assigned to the APN handling the request.

Figure 19 shows the configuration of IP address assignment based on APN.

Figure 19: IP Address Assignment Based on Access Point Name

Note: APN-based IP address assignment takes precedence over all other methods of IP address assignment except if an IP address (or pool name) is added to an Access-Accept as the value of the Framed-IP-Address attribute. For information about how to add any attribute from a subscriber database (such as a SQL database), see Adding Attributes to an Access-Accept. For example, you can retrieve the IP address from a SQL database and include it as the value of Framed-IP-Address in an Access-Accept.

Tasks for Assigning IP Address Based on Access Point

Assigning IP addresses based on access point involves the following main tasks:

• Configure simauth.aut
• Create an address pool

Each of these tasks is described in the following sections.

Configuring simauth.aut for IP Address Assignment

The simauth.aut configuration file retrieves the IP address from a pool to be returned with the Access-Accept.

To configure simauth.aut for IP address assignment based on access point:

1. In the [Settings] section of simauth.aut, define the attribute that identifies the access point. This attribute is usually 3GPP-WLAN-APN-Id or Called-Station-ID. Use the following format:
   
   AssignIpPoolByAttr = attribute

   where:

   attribute is the name of the string type attribute to be used to identify the access point.

   Example:

   [Settings]
   AssignIpPoolByAttr = 3GPP-WLAN-APN-Id

2. In the [Settings] section of simauth.aut, define the attribute to contain the IP address to be assigned to the mobile device. This attribute is returned with the Access-Accept. Use the following format:
   AssignIpPoolDestAttr = attribute_for_address

   where:

   attribute_for_address is the attribute used to return the IP address in the Access-Accept. This attribute must be consistent with an IPv4 IP address. (It is usually Framed-Ip-Address.)

   Example:

   [Settings]
   AssignIpPoolDestAttr = Framed-Ip-Address

3. In the [IpPools] section of simauth.aut, define the access point identifiers that associate specific pools with access points. Use the following format:
   attribute-value = poolname

   where:

   attribute-value is the access point identifier, and poolname is the name of an IP address pool created using the Web GUI.

   Example:

   [IpPools]
   ASN1 = Pool1
   ASN2 = Pool2
   * = Default_Pool

Figure 20 shows the configuration of simauth.aut for assigning IP addresses based on APN. In Figure 20, the access point is identified by the value of the attribute 3GPP-WLAN-APN-Id. If the value of 3GPP-WLAN-APN-Id is APN1, then an IP address is taken from pool1. If the value is neither APN1 nor APN2, the address is taken from the pool named default_pool. The IP address is assigned to the attribute Framed-IP-Address, which is returned in the Access-Accept message.

Figure 20: Configuration of IP Address Assignment Based on Access Point

Create the IP Address Pool

See the SBR Carrier Administration and Configuration Guide for more information about administering IP address pools.