NAC Tip: Cisco NAC XML Configuration File

Before version 4.6, the Cisco NAC Agent used registry key settings to for configuration.  Starting with version 4.6, the Cisco NAC Agent uses an XML file for configuration.  This file is located in c:Program FilesCiscoCisco NAC AgentNACAgentCFG.xml.  This configuration file provides many options for customizing the behavior of the NAC Agent.  Full details can be viewed in the Cisco NAC Manager Configuration Guide.

 

For a campus deployment, it is common to use the NAC Agent to detect the default gateway and then issue a DHCP release/renew if the default gateway is not available.  The NAC Agent does this by either using ICMP or ARP to connect to the default gateway and then issue a DHCP release/renew if the ICMP or ARPs fail a configurable number of times.  For example, if you wanted to use ICMP every 5 seconds and then issue the DHCP release/renew after 3 failures, the configuration would look like the XML configuration snippet below.

 

<VlanDetectInterval>5</VlanDetectInterval>

<RetryDetection>3</RetryDetection>

<PingArp>0</PingArp>

 

The VlanDetectInterval defines the timing between pings.  The RetryDetection determines the number of failures required before the DHCP release/renew.  The PingArp defines that ICMP is being used.  One point of note is that the case of the parameters is important.  This means that vlandetectinterval will not work.  You must use the proper case of VlanDetectInterval.

 

This configuration is installed along with the NAC Agent installation.  It is possible to make changes to the NACAgentCFG.xml centrally through the NAC Manager.  For example, you could change the RetryDetection from 3 failures to 4 failures on all NAC Agents through one change on the NAC Manager.  When the NAC Agent connects to a NAC server for NAC authentication and posture assessment, the first thing the NAC Server does is send the NAC Agent configuration file that is on the NAC Server.  The NAC Agent compares this configuration file with the file that exists locally and makes changes.  In general, the central NAC Agent configuration file only updates the local NAC Agent configuration file if the entry does not in the local NAC Agent configuration file.  If the entry did not exist in the local NAC Agent configuration file it means that it was using the default settings.  For example, if the central NAC Agent configuration file had 4 and there was no local NAC Agent configuration file entry, then the value would be added.  If the local NAC Agent configuration file had 2, then the entry would not be updated in the local NAC Configuration file and the value of 2 would remain.  In order to force a modification of the entry, an additional parameter needs to be added.  This parameter is called mode=”overwrite”.  For example, if the central NAC Agent configuration file had 4 then the local file would be changed to use the value 4. This is shown below.

 

<RetryDetection mode=”overwrite”>4</RetryDetection>

 

The steps below show how this is done.

1.  Login to the NAC Manager and access “Device Management > Clean Access > Clean Access Agent > Installation”

2.  Click the Installation Options for Windows

3.  Look at the “Agent configuration XML file upload” section

4.  If you had previously uploaded a configuration file, the “Download” button will be available.  This is a excellent way to keep track of the existing NAC Agent XML configuration file that is being deployed to end clients.  If this exists, download this version to modify its contents and upload.

5.  If configuration file had never been uploaded, then the “Download” button will not exist.  Open up wordpad to prepare to create a new NACAgentCFG.xml file for upload.

6.  At this point, the new configuration file is created.  This configuration file only needs to include the customized parameters.  Any parameters, not included, will follow the default values.  As mentioned above, this is the only place where the extra mode=”merge” and mode=”overwrite” parameters are used.  If nothing is added it is the same as saying mode=”merge”.  For this reason, the only parameter that you really need to add is mode=”overwrite”.

7.  Save the new configuration file

8.  In the NAC Manager click Browse and select the file just created, then click “upload”.  At this point the NAC Manager parses the file and ensures that the syntax is correct.  If the syntax is correct it returns a success meassage.

 

The next time a user logs in the new configuration file will be downloaded to their computer.  The configuration file will be compared to their existing configuration files.  If any downloaded configuration entries have the mode=”overwrite” parameter, they will be modified.  If any downloaded ocnfiguration entries do not exist locally, they will also be added.