The NAC labyrinth - part 2

Cisco's network control

Cisco's Network Admission Control can be directly mapped to TCG's NAC architecture. However, because Cisco is bound by the revenue reality of its installed base, the architecture comprises both in and extensions beyond what TCG offers.

On the client side, TCG's Network Access Requestor and the Trusted Network Connect client are covered by free Cisco Trust Agent software. TCG's Integrity Measurement Collectors appear in the Cisco model as vendor-provided agents and as (optionally) Cisco's own Cisco Secure Access product, a host intrusion-prevention system it picked up with its 2003 Okena acquisition.

Cisco has had to get serious about the protocols needed to handle Network Admission Control. At the lowest layer, Cisco selected the Extensible Authentication Protocol (EAP). While EAP was designed by the IETF for authentication and is used in most 802.1X deployments, Cisco has developed its own proprietary (but publicly disclosed) EAP method, called EAP-Fast (Flexible Authentication via Secure Tunneling). With EAP-Fast in place, Cisco can include 802.1X authentication as well as endpoint security assessment information wrapped inside the EAP protocol.

Because Cisco wants its product line to work with more than 802.1X-enabled switches, Cisco Trust Agent has EAP-over-802.1X and EAP-over-User Datagram Protocol (UDP) support. With this dual protocol support, when an end system tries to access the network using a method other than 802.1X, such as a VPN client or someone coming in through a non-802.1X switch, the EAP traffic travels over UDP instead of directly in Ethernet frames.

The critical difference between the 802.1X and UDP versions of Cisco's EAP: In the 802.1X case, EAP includes authentication and endpoint security assessment information. When used with UDP, Cisco's NAC no longer does authentication. Instead, the user has to be authenticated via some other mechanism, and the authentication and user credentials are no longer tightly tied to the security policy for that user.

This lack of symmetry between 802.1X and UDP versions of Cisco's Network Admission Control means that access and authentication are handled differently depending on whether you are connecting via LAN, wireless LAN or over a VPN tunnel.

A further symptom of this unequal support is the lack of wireless support in the free Cisco Trust Agent. For wireless 802.1X, network managers will have to replace the freeware Cisco Trust Agent 802.1X with a different 802.1X supplicant from Meetinghouse Data Communications or Funk Software (now Juniper). The real focus of the current version of Cisco's Network Admission Control is endpoint security assessment -- the authentication that comes out of the 802.1X dialogue is really a fortunate side effect.

As a dominant manufacturer of switches, routers and VPN devices, Cisco is shouldered with the difficult task of incorporating Network Admission Control into its devices. TCG's policy enforcement points equate in Cisco's architecture to network access devices. Cisco has pages of documentation explaining which devices will support the different client scenarios: EAP over UDP and EAP over 802.1X.

Summarizing those charts is difficult and subject to dissension: Cisco's competitors cite the requirement to upgrade all switches as a major disadvantage of Cisco's approach, while Cisco believes most enterprise customers interested in Network Admission Control have the right equipment in place and can start using it immediately.

One very clear issue is that the policy-enforcement capabilities of different devices vary widely. Sending full, fine-grained access control policies to the policy enforcement point will only be possible in networks with limited sets of devices, such as Cisco's high-end 6500 switches. Cisco's support of more coarse-grained access control, such as virtual LAN-based isolation or even wholesale go/no-go access to the network, comprises the capabilities of most Cisco products available today.

Cisco offers a second approach to its Network Admission Control with the Cisco Clean Access appliance, picked up with the 2004 Perfigo acquisition. This appliance is shoe-horned into Cisco's NAC strategy for companies that want endpoint security assessment, but don't want to change their infrastructure to get it. The long-term integration between the Clean Access server, the Clean Access agent and a general NAC scheme is uncertain, largely represented by malleable PowerPoint slides that are likely subject of ongoing debate within Cisco.

The Cisco equivalent to the TCG's back-end policy decision point is Cisco's access control server and a series of interfaces to third-party policy, authentication and audit servers. Access Control Server, Version 4.0 or higher, represents the Cisco version of a TCG network access authority combined with the Trusted Network Connect server. Integrity measurement verifiers, called policy server decision points in Cisco's architecture, connect to the Access Control Server using Cisco-defined protocols.

Cisco's architecture reaches beyond TCG's NAC plan with audit servers, which audit the endpoint security status of devices that do not have the Cisco Trust Agent installed on them. When an agentless system tries to connect to a network protected by Network Admission Control, the policy enforcement point (network access device in Cisco's terminology) can detect there is no agent. It then can sic an audit server on the end system, either by trying to scan the system from the outside or by trying to download agent software into the browser allowing an audit to occur. Although the audit server fills an architectural hole, it's not very clear how much useful data it will collect or whether it will be sufficient to set network access policies upon.

Cisco's Network Admission Control architecture is a serious one, and it is backed up by decent support throughout Cisco's product line. There are some ugly spots, though, such as the lack of policy integration when using non-802.1X methods. However, Cisco has struck a good balance between what is architecturally elegant and what works in existing enterprise networks. If there is a weak spot in Cisco's architecture, it's the intense focus on endpoint security and relative inattention paid to detailed access controls and authentication.

Join the newsletter!

Error: Please check your email address.

More about Access ServerACTCiscoDialogueFunk SoftwareHISIETFINSJuniper NetworksLogicalMeetinghouse Data CommunicationsMicrosoftOkenaOpus OneVIA

Show Comments

Market Place