Cisco Systems Uses, Requirements, and Limitations

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Cisco ASA 5500 Series Configuration Guide using ASDM
Chapter68 Configuring IKE, Load Balancing, and NAC
Configuring Network Admission Control Policies
You can configure the ASA to pass the IP address of the client to an optional audit server if the client
does not respond to a posture validation request. The audit server, such as a Trend server, uses the host
IP address to challenge the host directly to assess its health. For example, it may challenge the host to
determine whether its virus checking software is active and up-to-date. After the audit server completes
its interaction with the remote host, it passes a token to the posture validation server, indicating the
health of the remote host.
Following successful posture validation or the reception of a token indicating the remote host is healthy,
the posture validation server sends a network access policy to the ASA for application to the traffic on
the tunnel.
In a NAC Framework configuration involving the ASA, only a Cisco Trust Agent running on the client
can fulfill the role of posture agent, and only a Cisco Access Control Server (ACS) can fulfill the role of
posture validation server. The ACS uses dynamic ACLs to determine the access policy for each client.
As a RADIUS server, the ACS can authenticate the login credentials required to establish a tunnel, in
addition to fulfilling its role as posture validation server.
Note Only a NAC Framework policy configured on the ASA supports the use of an audit server.
In its role as posture validation server, the ACS uses access control lists. If posture validation succeeds
and the ACS specifies a redirect URL as part of the access policy it sends to the ASA, the ASA redirects
all HTTP and HTTPS requests from the remote host to the redirect URL. Once the posture validation
server uploads an access policy to the ASA, all of the associated traffic must pass both the Security
Appliance and the ACS (or vice versa) to reach its destination.
The establishment of a tunnel between a remote host and the ASA triggers posture validation if a NAC
Framework policy is assigned to the group policy. The NAC Framework policy can, however, identify
operating systems that are exempt from posture validation and specify an optional ACL to filter such
traffic.
Uses, Requirements, and Limitations
When configured to support NAC, the ASA functions as a client of a Cisco Secure Access Control
Server, requiring that you install a minimum of one Access Control Server on the network to provide
NAC authentication services.
Following the configuration of one or more Access Control Servers on the network, you must register
the Access Control Server group, using the Configuration > Remote Access VPN > Clientless SSL
VPN Access > Group Policies > Add or Edit External menu option. Then add the NAC policy.
ASA support for NAC Framework is limited to remote access IPsec and Clientless SSL VPN sessions.
The NAC Framework configuration supports only single mode.
NAC on the ASA does not support Layer 3 (non-VPN) and IPv6 traffic.
Fields
•Policy Name—Enter a string of up to 64 characters to name the new NAC policy.
Following the configuration of the NAC policy, the policy name appears next to the NAC Policy
attribute in the Network (Client) Access group policies. Assign a name that will help you to
distinguish its attributes or purpose from others that you may configure.
•Status Query Period—The ASA starts this timer after each successful posture validation and status
query response. The expiration of this timer triggers a query for changes in the host posture, referred
to as a status query. Enter the number of seconds in the range 30 to 1800. The default setting is 300.