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Comparing device configurations is one of NCM's most important features. You can use NCM to compare device configurations from one point in time to another. Or, when downloading a configuration, you can do a comparison and save the configuration only if there are differences.
In many cases, you want the comparison to ignore differences for certain lines. When you compare a running config to a startup config, the startup config sometimes has lines that start with
!Time). But the corresponding lines in the running config contain words or are blank. To prevent these lines from being identified as different, you can use a Regular Expression (RegEx) to tell NCM to ignore lines that begin with specific characters.
^!Timeignores all lines that begin with
!Time. To ignore any line that begins with
^!as the RegEx pattern.
To verify that the RegEx pattern provides the expected results, compare two configs that previously returned differences for lines that now should be ignored.
In order for charts and Config Change Reports to reflect that these lines are being ignored, download new configs for the devices where these lines were identified as different. When the tables in the database are updated, NCM will use the data to populate the charts and reports.
The following example shows some common differences found when NCM compares a running config to a startup config.
Line 1 -
! (no change)
Line 2 - the
!Last configuration change is not on the same line in the running config
Line 3 - the
!NVRAM is not on the same line in the running config
Line 4 - the
! is not on the same line in the running config
In order to have NCM ignore Line 4, you can add the RegEx pattern
^!, which ignores any line with a
! at the beginning. This pattern causes NCM to ignore all three lines, so you don't need separate RegEx patterns to ignore
! followed by another word, such as