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Using IAS proxy for load balancing

Updated: January 21, 2005

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Using IAS proxy for load balancing

This topic describes how IAS proxies, placed between access servers and IAS servers, can be used to balance the load of a large volume of authentication traffic. Without IAS proxies, each access server balances its RADIUS requests across multiple RADIUS servers and detects unavailable RADIUS servers. By using IAS proxy, consistent load balancing is used to spread the load of authentication, authorization, and accounting traffic across all the IAS servers in the organization. Additionally, there is a consistent scheme for failure detection and RADIUS server failover.

The following configuration is for an organization that uses:

  • Active Directory domains.

    Active Directory domains contain the user accounts, passwords, and dial-in properties that each IAS server requires to authenticate user credentials and evaluate both authorization and connection constraints. To optimize IAS authentication and authorization response times and minimize network traffic, IAS is installed on domain controllers.

  • Multiple IAS servers.

    To balance the load of RADIUS authentication, authorization, and accounting across multiple domain controllers, IAS is installed as a RADIUS server on them.

  • Remote access policies.

    Remote access policies are configured to specify, based on group membership, the different types of connection constraints for users.

  • Two IAS proxies.

    Two IAS proxies are used to provide fault tolerance for RADIUS requests that are sent from access servers.

The following illustration shows IAS proxies used to balance the load of RADIUS traffic across multiple IAS servers.

IAS in a perimeter network

Note

  • This topic only describes how to configure IAS. It does not describe the configuration of Active Directory domains or access servers. For more information about how to deploy these components, see the appropriate Help topics.

To configure IAS for this example, complete the following steps:

  • Configure the Active Directory forests for user accounts and groups.

  • Configure the IAS server on domain controllers.

  • Configure the primary IAS proxy.

  • Configure the secondary IAS proxy.

  • Configure RADIUS authentication and accounting on access servers.

Configuring forests for user accounts and groups

To configure Active Directory for user accounts and groups, do the following:

  1. Ensure that all users that are making network access connections have a corresponding user account.

  2. Manage your network access by group by setting the remote access permission on user accounts to Control access through Remote Access Policy. For more information, see Configure remote access permission for a user.

  3. Organize your remote access users into the appropriate universal and nested groups in order to take advantage of group-based remote access policies. For more information, see Group scope.

  4. If you are using the Challenge-Handshake Authentication Protocol (CHAP), enable support for reversibly encrypted passwords for the appropriate domains. For more information, see Enable reversibly encrypted passwords in a domain.

Configuring the IAS server on domain controllers

To configure IAS as a RADIUS server on each domain controller, do the following:

  1. On the domain controller, install IAS as an optional networking component. For more information, see Install IAS.

  2. Configure the IAS server computer (the domain controller) to read the properties of user accounts in the domain. For more information, see Enable the IAS server to read user accounts in Active Directory.

  3. If the IAS server authenticates connection attempts for user accounts in other domains, verify that the other domains have a two-way trust with the domain in which the IAS server computer is a member. Next, configure the IAS server computer to read the properties of user accounts in other domains. For more information, see Enable the IAS server to read user accounts in Active Directory. For more information about trust relationships, see Trust direction.

  4. Enable file logging for accounting and authentication events. For more information, see Configure log file properties.

  5. Add the IAS proxies as RADIUS clients of the IAS server. For more information, see Add RADIUS clients. Verify that you are configuring the correct name or IP address and shared secrets. For more information, see Shared secrets.

  6. Create the appropriate remote access policies for access clients.

    For examples of remote access policies, see Remote Access Policies Examples.

Configuring the primary IAS proxy

To configure the primary IAS proxy, do the following:

  1. On a computer running Windows Server 2003, Standard Edition; Windows Server 2003, Enterprise Edition; or Windows Server 2003, Datacenter Edition; install IAS as an optional networking component. For more information, see Install IAS. The computer on which IAS is installed is not required to be dedicated to forwarding RADIUS messages. For example, You can install IAS on a Web server, file server, or DNS server.

  2. If needed, configure additional UDP ports for RADIUS messages that are sent by the access servers. For more information, see Configure IAS port information. By default, IAS uses UDP ports 1812 and 1645 for authentication and ports 1813 and 1646 for accounting.

  3. Add the access servers as RADIUS clients of the IAS server. For more information, see Add RADIUS clients. Verify that you are configuring the correct name or IP address and shared secrets. For more information, see Shared secrets.

  4. Use the New Remote RADIUS server Group Wizard to create a custom remote RADIUS server group. Add each IAS server as a member of the remote RADIUS server group and configure each group member with the priority of 1 and a weight of 50.

  5. Create a connection request policy that forwards RADIUS request messages to the IAS servers where the realm name matches the accounts in the domain.

    Use the New Connection Request Policy Wizard to create a connection request policy that forwards connection requests to a remote RADIUS server and where the realm name matches the realm name for the user accounts in the forest. Clear the check box that removes the realm name for authentication. Select the previously created remote RADIUS server group as the group to forward connection requests.

    For more information, see Add a connection request policy.

  6. Delete the default connection request policy named Use Windows authentication for all users. For more information, see Delete a connection request policy.

Configuring the secondary IAS proxy

To configure the secondary IAS proxy on another computer, do the following:

  1. On another computer running Windows Server 2003, Standard Edition; Windows Server 2003, Enterprise Edition; or Windows Server 2003, Datacenter Edition; install IAS as an optional networking component. For more information, see Install IAS.

  2. Copy the configuration of the primary IAS proxy to the secondary IAS proxy. For more information, see Copy the IAS configuration to another server.

Configuring RADIUS authentication and accounting on the access servers

To configure each access server to use the primary and secondary IAS proxies for the authentication, authorization, and accounting of network connections, do the following:

  1. If the dial-up or VPN server is a computer running Windows Server 2003, Standard Edition; Windows Server 2003, Enterprise Edition; Windows Server 2003, Datacenter Edition; or Windows 2000 and the Routing and Remote Access service, configure the primary and secondary IAS proxies as RADIUS servers for both RADIUS authentication and accounting. For more information, see Use RADIUS authentication and Use RADIUS accounting.

  2. If the dial-up or VPN server is a computer running Windows NT server 4.0 and the Routing and Remote Access Service (RRAS), see the Windows NT server 4.0 online Help for information about how to configure the primary and secondary IAS proxies as RADIUS servers for RADIUS authentication.

  3. If the dial-up or VPN server is a third-party access server, see the documentation for the access server to determine how to configure it as a RADIUS client with two RADIUS servers (the primary and secondary IAS proxies).

Note

  • You can configure IAS in Windows Server 2003, Standard Edition, with a maximum of 50 RADIUS clients and a maximum of 2 remote RADIUS server groups. You can define a RADIUS client using a fully qualified domain name or an IP address, but you cannot define groups of RADIUS clients by specifying an IP address range. If the fully qualified domain name of a RADIUS client resolves to multiple IP addresses, the IAS server uses the first IP address returned in the DNS query. With IAS in Windows Server 2003, Enterprise Edition, and Windows Server 2003, Datacenter Edition, you can configure an unlimited number of RADIUS clients and remote RADIUS server groups. In addition, you can configure RADIUS clients by specifying an IP address range.

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