I’ve written before in Subsystem Configuration Policy Check about incorporating operational data with configurations for performing configuration compliance validation. Another example, with a different twist to it, occurred last week while creating an NTP policy check on a customer’s network. The NTP design is three layers. There are two stratum 1 clocks, one per data center. Within each data center is a core 6500 that uses the master clock within the data center as its clock source. There is a large set of distribution layer devices that reference the core 6500s as ntp servers using the following configuration:
ntp server 10.1.1.1 ! Datacenter 1 6500 ntp server 10.1.2.1 ! Datacenter 2 6500
Validating the configurations of the distribution layer devices is pretty easy. Create a device group of all core and distribution devices, exclude the two core 6500s, and check that the configurations include the above commands. It is good practice to make sure that there are no other NTP configuration statements in the configs.
The catch comes with the edge devices. The network is running MPLS and the CE devices may not have a route to the core 6500s. So the CE devices are configured to use their neighboring PE devices (the distribution layer), as their clock source. The IP address in the NTP configuration statement depends on the address of the neighbor. The configuration policy validation system needs to run some commands on the CE device to determine the PE’s address (e.g., show cdp neigh detail), then check the configuration for the NTP statement that uses that address. This is a simple case of configuration compliance; I envision some configuration checks that might need the output and merger of multiple commands in order to determine the required configuration statements.
The important concept with this example is that configuration policy checking isn’t just about looking for a few commands in the configuration. The policy compliance system needs the ability to incorporate operational and as-built data into its compliance checks.
-Terry
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Re-posted with Permission
NetCraftsmen would like to acknowledge Infoblox for their permission to re-post this article which originally appeared in the Applied Infrastructure blog under http://www.infoblox.com/en/communities/blogs.html
