Basic Enterprise Mobility – Strategy

Extending the enterprise’s wired LAN to wireless is one of the more straightforward tasks from a network design perspective, but the authentication piece for the Wireless LAN needs to be strictly controlled.  Fortunately, wireless can benefit from the widespread deployment of another technology in the enterprise world – centralized authentication servers.

Many enterprise environments utilize a centralized authentication system to manage their user accounts, with Microsoft Active Directory being one of the most common.  This system can also be leveraged to provide authentication to the Wireless LAN.  Active Directory can serve as an 802.1X authenticator, allowing the wireless network to use EAP technology to authenticate users.  The two EAP methods most worthy of consideration in a WLAN environment are EAP-TLS, and PEAP.

EAP-TLS provides full mutual authentication, using a public key infrastructure to create and manage certificates for both client devices and the authenticating server.  In practice, it will allow users to seamlessly authenticate to the wireless network, because the certificate exchange occurs behind the scenes.  In an Active Directory environment, the certificates used in authentication can be deployed remotely by the Domain Controllers.  This works especially well with laptop users, but can be a challenge with mobile devices that do not have a wired connection to the network.  Certificates can be pushed to mobile devices in several ways, such as by use of a dedicated management WLAN or physical installation via memory cards or barcode scanning, but in a large environment with many mobile devices, it may be wise to look into alternatives.

Fortunately, a worthy alternative to EAP-TLS exists with PEAP authentication.  PEAP provides for similar levels of security to EAP-TLS, but does not rely on client certificates to authenticate devices to the network.  Instead, PEAP uses a more traditional username & password combination.  These credentials can be integrated with an Active Directory environment, allowing administrators granular control over what users get access to the WLAN.  PEAP also mitigates the potentially expensive maintenance cost of managing certificates on mobile devices.

EAP-TLS and PEAP, combined with WPA2-AES, provide the strongest authentication and encryption solutions available in WLAN, and as such should be used to protect any critical data traveling over the network.  While integration with Active Directory is not mandatory, because many organizations have such an environment already deployed, extending its use to cover WLAN authentication is an attractive option.  If your organization does not have a centralized authentication system in place already, the deployment of a WLAN can be a strong motivation to do so.  Several free alternatives to Active Directory also exist, such as FreeRADIUS.  Some enterprise-grade WLAN infrastructure also provides the ability to generate and manage certificates using an internal server hosted on the access point.  Given the easy integration with common authentication systems, and the availability of free alternatives, there really is no reason not to deploy a centralized authentication solution to secure your enterprise WLAN.

Pre-Shared Keys – also known as “Personal” authentication – are generally not appropriate for enterprise environments.  WPA2-AES using pre-shared keys does not have any documented vulnerabilities, but any PSK solution relies on sharing authentication credentials between multiple users and devices.  This can affect the integrity of the network, and doesn’t provide any traceability to activities of users on the network.  It should be avoided in a mission-critical environment.

Depending on the size and business needs of the enterprise, a WLAN can be used in a few different ways:

Basic Mobility – the most common use of WLAN is simply to extend the existing wired LAN to wireless users.  This can have a very positive impact on productivity, allowing users more flexibility throughout the workspace.

Segmented Mobile Data - this type of WLAN is one where the network is dedicated to use of a specific type of data that is segmented from the main enterprise network.  Typical use cases here are in hospitals or retail stores, where compliance regulations provide strict guidance on data protection and segmentation.

Guest Internet Access – common in cafes and large businesses, this type of WLAN typically provides only internet access and is entirely segmented from the enterprise wired LAN.

Wired LAN Replacement - this type of network is becoming a feasible alternative to the hassle of running cable, and will likely continue to grow in popularity as time goes by

These use cases can blend together in any number of ways.  A well thought-out design at the beginning, along with the right hardware planning, can accomidate these uses and even more.

General Strategy

Like other networking strategies, the use of proper segmentation at the Layer 2 level is critical when designing a WLAN.  Your most critical data flows should have their own segment, protected by methods like VLAN segmentation, firewalling, private IP spaces, and routing tables.  Regardless of the authentication and encryption method used for the WLAN itself, properly designing its location within the enterprise wired LAN is critical.

Data encryption in 802.11 is accomplished by a combination of the authentication type with an underlying encryption method.  Use of WPA2-AES encryption should be considered mandatory in any new WLAN deployment.  This encryption technology has no documented vulnerabilities and widespread hardware and software support.  If your enterprise has devices that do not support WPA2-AES, strongly consider replacing them.  When designing a network, its security should not be determined by the weakest link.  Unless there is a business case for doing something otherwise, use the strongest encryption and authentication methods available.

My next post will get into some specifics about these different use cases!

Some History

I will not go into the history of the 802.11 standard in too much detail here, although there are a couple of important points to recognize when thinking about how to deploy a WLAN in your business.  The most important thing to know is this – many of the WLAN security technologies that were being used in deployment until three or four years ago are vulnerable to several well-known attacks.  If your business has a WLAN that has “just been working” for a while – it should probably get some attention.

To elaborate on this a bit further, the most common Wireless LAN encryption method used until late 2003, WEP, has been subject to some very public weaknesses, almost since its inception.  Its temporary replacement, WPA-TKIP, has similar (although not as dramatic) weaknesses, that have been public since at least 2008.

Adding insult to these platform-common weaknesses, some of the alternate, “more secure” based authentication methods advised by vendors have also been picked apart and had their vulnerabilities shown to the world.  I’m looking at you, LEAP.

To sum it up briefly – many networks that people thought were secure in 2003 or 2004 are definitely not secure today.  And unfortunately, WLAN sometimes is treated like a part of the physical infrastructure – if it ain’t broke, don’t fix it!

Current Tech

Fortunately, 802.11 is really starting to come into its own lately, and can be an extremely secure – in some ways more secure – piece of critical infrastructure.  The extremely solid (and so far unbroken) WPA2-AES encryption standard defined by 802.11i has had widespread vendor support since 2007.  And certificate-based authentication methods such as EAP-TLS, PEAP, and EAP-TTLS have similarly experienced a growth in support, among not just desktop OS platforms, but mobile operating systems as well.  And Wireless Intrusion Detection Systems are hitting their stride, ranging from several robust and effective professional solutions from vendors like AirTight, Cisco, and Motorola, to fantastic open-source applications like Kismet.  And robust infrastructure management software is now making the administration of Wireless LANs more simple and effective.

In short, today it is possible to deploy a WLAN that will meet all the use cases an enterprise can throw at it, and that is as secure as a typical wired LAN infrastructure.

In the next post, I’ll cover typical enterprise WLAN use cases, and the strategies for designing and securing them.

I recently had the opportunity to speak with a WLAN network administrator and we briefly discussed the merits of using an integrated RADIUS server on APs vs using an external RADIUS server for authentication. After thinking about it for a few days, I realized that relying solely on the integrated RADIUS server for wireless authentication is rarely a good idea.

• Integrated RADIUS servers on APs are typically minimal servers that are designed to serve a small number of clients. If the WLAN network grows in size, the number of users that will need to be configured could easily exceed the limits of the integrated RADIUS servers.
• Some integrated RADIUS servers do not offer support for accounting services. This can be either a non-issue or a serious disadvantage depending on the purpose of the WLAN.
• Integrated RADIUS servers typically use proprietary local database engines/management interfaces to administer the user database, which makes it difficult to do certain operations like import/export user databases between APs or switch to APs from a different vendor.
• Standalone RADIUS servers offer advanced capabilities such as integrating with LDAP or Exchange servers to provide single sign-on capabilities. Integrated RADIUS servers in APs don’t have such capabilities due to the complexities and necessary protocol support required to interact with other authentication servers.
• Integrated RADIUS servers can only support the EAP methods that are built into it, restricting the set of EAP methods that can be used in the WLAN. Standalone RADIUS servers can typically support a much larger number of EAP methods and therefore provide the WLAN administrator with a great deal of flexibility. Note that APs which are acting only as a NAS are only relaying EAP messages between clients and the RADIUS server and therefore don’t need to have support for the different EAP types built-in.

However, even with all of the advantages a standalone RADIUS server offers over an integrated RADIUS server, there are some compelling advantages of the integrated solution: the integrated server is likely only to fail when the AP itself physically fails, the authentication sequence may be slightly faster since there is no extra hop between the AP and a RADIUS server, and of course it doesn’t require any additional capital expense for your network. In short, the decision between a integrated and standalone server solution should carefully consider short term and long term costs/network growth as well as flexibility in supporting both existing and future requirements of the network.

I define subscriber to subscriber traffic filtering as a network design which explicitly prohibits the exchange of packets directly between subscribers without first passing those packets through a firewall or access control lists. An example of this type of network is a typical cable or DSL service network provider where subscriber packets are filtered through a network access server (NAS) prior to being forwarded to their destinations. A metro Ethernet network is an example of a network that does NOT perform peer to peer traffic filtering (metro Ethernet provides layer 2 connectivity between subscribers).

From a pure service provider business perspective, you care little about the types of traffic that subscribers exchange as long as you are able to meet the SLAs that you have established. If the traffic that is exchanged happens to contain malicious information (viruses, malware etc.), the service provider isn’t really going to care as the type of traffic exchanged doesn’t affect their ability to provide service to subscribers.

From a subscriber perspective, you care a lot about whether or not your home/business network is subjected to malicious traffic originating from your outside network connection. However, you also care about having the freedom to use your outside network connection as a raw pipe and being able to exchange any kind of network traffic with anybody that you can connect to (especially home users who use BitTorrent and other P2P protocols).

From a regulatory perspective, as a service provider you care about meeting the legal requirements to provide service in the regions you operate in order to avoid penalties etc. Certain governments impose restrictions on the types of traffic that network users are allowed to exchange (China being a prime example with strict requirements on which websites can be viewed by Chinese residents).

As can be seen from these 3 different perspectives, the need to implement filtering controls to restrict subscriber to subscriber traffic is not immediately evident. From a security threat perspective, most service provider networks are designed to provide clean seperation of bearer data (subscriber traffic) and control/management data used by the provider to run their network. So the risk of subscribers actually accessing the service provider’s infrastructure is quite low. A slightly more obvious security threat is the risk of being non-compliant to regulatory requirements. In this case, the risk of non-compliance can be quite high depending on each country’s regulations.

In conclusion, when considering whether or not to implement peer to peer traffic filtering and whether or not the lack of this filtering is a security risk, consider the network design and the regulatory requirements governing the network operation. You may be surprised to find that there is in fact little to no security risks to the service provider by NOT performing peer to peer traffic filtering.