Configuration Replace
The
configure replace
privileged EXEC command provides the capability to replace the current running
configuration with any saved Cisco IOS configuration file. This functionality can be used to revert to a previous
configuration state, effectively rolling back any configuration changes that were made since the previous
configuration state was saved.
When using the
configure replace
command, you must specify a saved Cisco IOS configuration as the
replacement configuration file for the current running configuration. The replacement file must be a complete
configuration generated by a Cisco IOS device (for example, a configuration generated by the
copy
running-config destination-url
command), or, if generated externally, the replacement file must comply with
the format of files generated by Cisco IOS devices. When the
configure replace
command is entered, the
current running configuration is compared with the specified replacement configuration and a set of diffs is
generated. The algorithm used to compare the two files is the same as that employed by the
show archive
config differences
command. The resulting diffs are then applied by the Cisco IOS parser to achieve the
replacement configuration state. Only the diffs are applied, avoiding potential service disruption from reapplying
configuration commands that already exist in the current running configuration. This algorithm effectively
handles configuration changes to order-dependent commands (such as access lists) through a multiple pass
process. Under normal circumstances, no more than three passes are needed to complete a configuration
replace operation, and a limit of five passes is performed to preclude any looping behavior.
The Cisco IOS
copy source-url running-config
privileged EXEC command is often used to copy a stored
Cisco IOS configuration file to the running configuration. When using the
copy source-url running-config
command as an alternative to the
configure replace target-url
privileged EXEC command, the following
major differences should be noted:
• The
copy source-url running-config
command is a merge operation and preserves all of the commands
from both the source file and the current running configuration. This command does not remove commands
from the current running configuration that are not present in the source file. In contrast, the
configure
replace target-url
command removes commands from the current running configuration that are not
present in the replacement file and adds commands to the current running configuration that need to be
added.
• The
copy source-url running-config
command applies every command in the source file, whether or
not the command is already present in the current running configuration. This algorithm is inefficient
and, in some cases, can result in service outages. In contrast, the
configure replace target-url
command
only applies the commands that need to be applied—no existing commands in the current running
configuration are reapplied.
• A partial configuration file may be used as the source file for the
copy source-url running-config
command, whereas a complete Cisco IOS configuration file must be used as the replacement file for the
configure replace target-url
command.
A locking feature for the configuration replace operation was introduced. When the
configure replace
command is used, the running configuration file is locked by default for the duration of the configuration
replace operation. This locking mechanism prevents other users from changing the running configuration
while the replacement operation is taking place, which might otherwise cause the replacement operation to
terminate unsuccessfully. You can disable the locking of the running configuration by using the
no lock
keyword when issuing the
configure replace
command.
The running configuration lock is automatically cleared at the end of the configuration replace operation. You
can display any locks that may be currently applied to the running configuration using the
show configuration
lock
command.
System Management Configuration Guide, Cisco IOS XE Gibraltar 16.10.x (Catalyst 9200 Switches)
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Configuration Replace and Configuration Rollback
Configuration Replace