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The Building Blocks in a Cisco NAC Appliance Design

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Jul 8, 2008.

Chapter Description

This chapter focuses on the building blocks available with the Cisco NAC Appliance solution. The purpose and function of each piece is covered, as are the requirements, scalability, and performance of these building blocks.

This chapter covers the following topics:

  • Cisco NAC Appliance Solution Components
  • Cisco NAC Appliance Minimum Requirements
  • Scalability and Performance of Cisco NAC Appliance

Knowledge of how to properly design security solutions is what separates the professional from the amateur. Without a proper design, the eventual implementation will most likely be a disaster. One of the keys to success when designing a security solution is to first understand all the pieces you have to work with. I like to call these building blocks. After you achieve understanding, you then need to become skilled at manipulating the pieces in ways that best fit your environment. This chapter focuses on the building blocks available with the Cisco NAC Appliance solution. The purpose and function of each piece is covered. The requirements, scalability, and performance of these building blocks are also discussed. The next chapter discusses your options for manipulating these building blocks.

Cisco NAC Appliance Solution Components

A NAC Appliance solution is made up of the following components:

  • Mandatory components:
    • - Cisco NAC Appliance Manager (Clean Access Manager)
    • - Cisco NAC Appliance Server (Clean Access Server)
  • Optional components:
    • - Cisco Clean Access Agent
    • - Cisco NAC Appliance Network Scanner

Each piece has a distinct role to play in the solution. In this section, you examine the roles of each in more detail.

Cisco NAC Appliance Manager

The roles of NAC Appliance Manager are as follows:

  • Central administration and monitoring
  • Management of up to 40 NAC Appliance Server pairs
  • Central configuration of security policy and requirements
  • Performing automatic download of the latest Clean Access policies and updates
  • Centrally controlling network devices
  • Central user authentication to back-end authentication sources such as Lightweight Directory Access Protocol (LDAP), RADIUS, and Kerberos

NAC Appliance Manager is the administration server. It allows you to centrally manage and monitor your deployment of NAC Appliance Servers and Agents. It is here that you configure your security policies that define the checks your hosts will have to pass to be considered clean or up to date. The NAC Appliance allows you to build your own customized checks, but it also comes with many preconfigured checks. It is a big job to manually maintain and track all the new updates that come out for antivirus, antispyware, Microsoft Windows, and so on. That is why the NAC Appliance Manager is also responsible for receiving regular version and policy updates from Cisco. These policy updates contain information on the latest operating system patches, antivirus versions, and antispyware versions. The prepackaged software checks and security policies are automatically updated with this new version information. Using the policy update feature makes it easier to ensure your hosts are always checked for the latest versions before they are allowed network access.

NAC Appliance Manager is configured using a web console after a minimal bootstrapping process. NAC Appliance Manager is capable of scaling to administer up to 40 NAC Appliance Server pairs. NAC Appliance Manager's web console allows you to configure both global security policies and per-server local policies. Global security policies save time and are much easier to manage. For example, you could create a global policy that says all hosts connecting to the network through any NAC Appliance Server must have an up-to-date antivirus program installed. NAC Appliance Manager then pushes this policy out to all the NAC Appliance Servers for local checking and enforcement. If you have some specific local security policies that pertain to only a single NAC Appliance Server, you can use NAC Appliance Manager's web console to configure those as well. Figure 3-1 shows NAC Appliance Manager's web console.

Figure 3-1

Figure 3-1 NAC Appliance Manager Web Console

NAC Appliance Manager is responsible for authenticating all users in the NAC Appliance deployment with the exception of single sign-on (SSO) users. SSO users are authenticated by the local NAC Appliance Server. NAC Appliance Manager can use either its local user database or an external user database such as LDAP or RADIUS as an authentication source.

Cisco NAC Appliance Server

The roles of the NAC Appliance Server are as follows:

  • Security policy assessment
  • Security policy enforcement

NAC Appliance Server is the policy enforcer, or the policy firewall, between the untrusted networks and the trusted networks. NAC Appliance Server's job is to enforce the security policies created in NAC Appliance Manager. NAC Appliance Server, in conjunction with NAC Appliance Manager, actively checks the identity of users and the security posture of their host when they try to obtain access to the network. Based on the results of the check, NAC Appliance Server enforces the proper network access policy. It is important to note that NAC Appliance Server and NAC Appliance Manager act as a team in this process. NAC Appliance Server is mostly responsible for asking for authentication and posture information from the clients. This information is then forwarded to NAC Appliance Manager for checking. Based on the results, NAC Appliance Manager instructs the server to start enforcing a particular policy for that client.

For NAC Appliance Server to work, it must be physically or logically inline between the clients and their destinations during the initial posture assessment and remediation. After the clients pass the posture assessment, NAC Appliance Server can be removed from the dataflow (out of band) or remain in the dataflow (in band). The next chapter will discuss these different options in detail.

Clients can use either the Clean Access Agent or web login to trigger NAC Appliance posture assessment. Figure 3-2 illustrates the steps that trigger inspection of a client with a Clean Access Agent preinstalled.

Figure 3-2

Figure 3-2 Steps to Trigger Assessment Using a Clean Access Agent

The following is an explanation of the numbered process in Figure 3-2.

  • Step 1 The host plugs into a switch port and requests a DHCP address. Acting as the DHCP server, NAC Appliance Server replies to the host's DHCP request. Clean Access Agent detects the new network connection.
  • Step 2 To find NAC Appliance Server, Clean Access Agent sends out discovery packets to all the default gateways present in the host's routing table. In Figure 3-2, NAC Appliance Server is the host's default gateway and receives the discovery packets.
  • Step 3 The discovery packets trigger NAC Appliance Server to perform assessment of the new host. First it checks to see whether the host MAC address is already permitted. If so, the host is allowed to pass through NAC Appliance Server. If not, NAC Appliance Server sends back a login request to Clean Access Agent.
  • Step 4 Clean Access Agent pops up the agent log in a dialog box and waits for the user to enter a username and password.

Figure 3-3 illustrates the steps that trigger inspection of a client using the web login.

Figure 3-3

Figure 3-3 Steps to Trigger Assessment Using Web Login

The following is an explanation of the numbered process in Figure 3-3.

  • Step 1 The host plugs into a switch port and requests a DHCP address. Acting as the DHCP server, NAC Appliance Server replies to the host's DHCP request.
  • Step 2 The user launches a web browser and requests a website. NAC Appliance Server sees this request. It checks the MAC address or IP address of the host to see whether it is already permitted. If so, the host is allowed on the network. If not, NAC Appliance Server intercepts the web request.
  • Step 3 The web page request triggers NAC Appliance Server to perform assessment of the host. The intercepted web page request is stopped, and a redirect to NAC Appliance Server's web login page is sent back to the user's web browser.
  • Step 4 The user is redirected and presented with the web login page. NAC Appliance Server waits for the client to log in or click on guest access.

NAC Appliance Manager's web console is used to centrally manage NAC Appliance Servers. However, each server does have a local web console and supports Secure Shell (SSH). These can be useful for troubleshooting purposes but are not generally used for local configuration after NAC Appliance Server's initial setup script is run.

Cisco Clean Access Agent

Technically, Clean Access Agent and Network Scanner are optional components. However, in most cases, you will use the Clean Access Agent and Network Scanner in your deployment.

Clean Access Agent is a free software program that resides on client PCs. It is a read-only agent whose job is to gather information about the user and the host it is installed on. It then matches that against the requirements received for that user, role, or OS from NAC Appliance Server and sends back a report to NAC Appliance Manager via NAC Appliance Server. If the requirements are met, the host is allowed on the network. If the host fails, Clean Access Agent presents the user, via a dialog box, with the remediation instructions received from NAC Appliance Manager. The information it checks for is configured by you at the NAC Appliance Manager level and then pushed out to each NAC Appliance Server. The information that can be checked by Clean Access Agent includes applications, files, registry keys, and services. For example, Clean Access Agent could check for the presence of a Windows hotfix or check to see whether an antivirus program is current.

Hosts that fail a system check are then put into a Clean Access Agent Temporary role. This role is configured to restrict network access to only those resources they will need to remediate their host. This may include access to websites, such as update.microsoft.com, or access to antivirus vendor update servers (local or on the Internet). These restrictions are enforced at the closest NAC Appliance Server in the traffic path of Clean Access Agent. No enforcement is done locally at the Clean Access Agent level. Clean Access Agent will then help the user fix up, or remediate, the host. It uses pop-up dialog boxes to notify the user of security policy violations that have occurred. It also provides a remediation button to fix the violation. See Figure 3-4 for an example.

Figure 3-4

Figure 3-4 Clean Access Agent Remediation Example

Cisco NAC Appliance Network Scanner

Network Scanner allows you to scan hosts to check for known vulnerabilities. Network Scanner is integrated into the NAC Appliance Manager and NAC Appliance Server software and is not a standalone piece. Network Scanner uses Nessus to scan hosts. You add in the Nessus plug-ins of your choice. For example, you can add the plug-ins that check to see whether music file-sharing applications are running on the host. If such programs are running, you could notify the end users that they must disable or uninstall the offending software before they are allowed on the network. Network Scanner can also be used to posture assess hosts that run operating systems not supported by Clean Access Agent, such as Linux.

The following simple example illustrates where the pieces of a Cisco NAC Appliance design are placed in a network. Figure 3-5 shows a NAC Appliance deployment using Layer 2 in-band. Layer 2 means that NAC Appliance Server is Layer 2 adjacent to the clients it will control. In-band means that data traffic always flows through NAC Appliance Server.

Figure 3-5

Figure 3-5 Cisco NAC Appliance Deployment Example (Layer 2 In-Band)

2. Cisco NAC Appliance Minimum Requirements | Next Section

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