The configuration replace feature enables you to replace the running configuration of the Cisco Nexus switch with the user provided configuration without reloading the device. The device reload may be required only when a configuration itself requires a reload. The running configuration file that is provided by the user should be taken using copy running file. Unlike copy file: to running, the configuration replace feature is not a merge operation. This feature replaces the entire running configuration with a new configuration that is provided by the user. If there is a failure in the configuration replace, the original configuration is restored in the switch. From Cisco NX-OS Release 9.3(1), best-effort option is introduced. This option enables the configuration replace to execute the full patch despite any error in the commands and the original configuration is not restored in the switch.

The commit-timeout feature enables you to rollback to the previous configuration after successfully performing the configuration replace operation. If the commit timer expires, the rollback operation is automatically initiated.

Note	You must provide a valid running configuration that has been received with the Cisco NX-OS device. It should not be a partial configuration.

The configuration replace feature has the following operation steps:

• Configuration replace intelligently calculates the difference between the current running-configuration and the user-provided configuration in the Cisco Nexus switch and generates a patch file which is the difference between the two files. You can view this patch file which includes a set of configuration commands.

• Configuration replace applies the configuration commands from the patch file similarly to executing commands.

• The configuration rolls back to or restores the previous running configuration under the following situations:

  • If there is a mismatch in the configuration after the patch file has been applied.

  • If you perform the configuration operation with a commit timeout and the commit timer expires.

• The configuration does not roll back to or does not restore the previous running configuration when the best-effort option is used. This option enables the configuration replace to execute the full patch despite any error in the commands and will not roll back to the previous configuration.

• You can view the exact configuration that caused a failure using the show config-replace log exec command.

• Restore operations that fail while restoring the switch to the original configuration, are not interrupted. The restore operation continues with the remaining configuration. Use the show config-replace log exec command to list the commands that failed during the restore operation.

• If you enter the configure replace commit command before the timer expires, the commit timer stops and the switch runs on the user provided configuration that has been applied through the configuration replace feature.

• If the commit timer expires, roll back to the previous configuration is initiated automatically.

• In Cisco NX-OS Release 9.3(1), semantic validation support is added for the configuration replace. This semantic validation is done as part of the precheck in configuration replace. The patch gets applied only when the semantic validation is successful. After applying the patch file, configuration replace triggers the verification process. The configuration replace compares the running-configuration with the user configuration file during the verification process. If there is a mismatch, it restores the device to the original configuration.

The differences between configuration replace and copying a file to the running-configuration are as follows:

The configuration replace feature has the following configuration guidelines and limitations:

• The configuration replace feature is supported on Cisco Nexus 3000 Series and Cisco Nexus 9000 Series switches.

• Only one user can perform the configuration replace, checkpoint, and rollback operations, or copy the running-configuration to the startup configuration at the same time. Parallel operations such as operations via multiple Telnet, SSH, or NX-API sessions are not supported. The multiple configuration replace or rollback request is serialized, for example, only after the first request is completed, processing of the second request begins.

• You are not allowed to initiate another configuration replace operation when the commit timer is running. You must either stop the timer by using the configure replace commit command or wait until the commit timer expires before you initiate another configuration replace operation.

• When system default switchport shutdown or no system default switchport shutdown is used with configure replace bootflash:target_config_file command, the user should make sure that desired port state (shutdown or no shutdown) statement is present in the target_config_file for all switchport interfaces.

• The commit-timeout feature is initiated only if you perform the configuration replace operation with the commit-timeout. The timer value range is from 30 to 3600 seconds.

• The user provided configuration file must be the valid show running-configuration output that is taken from the Cisco NX-OS device (copy run file). The configuration cannot be a partial configuration and must include mandated commands, such as user admin and so on.

• We do not recommend a configuration replace operation that is performed on the configuration file that is generated across the software version because this operation could fail. A new configuration file must be regenerated whenever there is change in the software version.

• We recommend that you do not change any configuration from others sessions if the configuration replace operation is in progress because it could cause the operation to fail.

• Note the following about the configuration replace feature:

  • The configuration replace feature is not supported on Cisco Nexus 9500 platform switches with -R line cards.

  • The configuration replace feature could fail if the running configuration includes the feature-set mpls or the mpls static range commands and tries to move to a configuration without MPLS or modifies the label range.

  • The configuration replace feature does not support autoconfigurations.

• If the line card to which the configuration replace feature is applied is offline, the configuration replace operation fails.

• If your configurations demand reloading the Cisco NX-OS device in order to apply the configuration, then you must reload these configurations after the configuration replace operation.

• The order of the commands in the user provided configuration file must be the same as those commands in the running configuration of the Cisco Nexus switch.

• The user configuration file to which you need to replace the running configuration on the switch using CR should be generated from the running-config of the switch after configuring the new commands. The user configuration file should not be manually edited with the CLI commands and the sequence of the configuration commands should not be altered.

• The semantic validation is not supported in 4-Gig memory platforms.

• When different versions of a feature are present in the running configuration and user configuration (for example: VRRPv2 and VRRPv3), semantic validation option does not work as expected. This issue is a known limitation.

The following workflow is the recommended workflow for configuration replace:

To check and verify configuration replace and its status, use the commands that are outlined in the table:

See the following configuration examples for configuration replace:

• Use the configure replace bootflash: <file> show-patch CLI command to display the difference between the running-configurations and user-provided configurations.

  switch(config)# configure replace bootflash:<file> show-patch 
  Collecting Running-Config
  Converting to checkpoint file
  #Generating Rollback Patch
  !!                                                                 
  no role name abc

• Use the configure replace bootflash: <file> verbose CLI command to replace the entire running-configuration in the switch with the user-configuration.

  switch(config)# configure replace bootflash:<file> verbose 
  Collecting Running-Config
  Generating Rollback patch for switch profile
  Rollback Patch is Empty
  Note: Applying config parallelly may fail Rollback verification
  Collecting Running-Config
  #Generating Rollback Patch
  Executing Rollback Patch
  ========================================================
  config t
  no role name abc
  ========================================================
  Generating Running-config for verification
  Generating Patch for verification
  
  Rollback completed successfully.
  
  Sample Example with adding of BGP configurations.
  	switch(config)# sh run | section bgp
  	switch(config)# sh file bootflash:file | section bgp
  feature bgp
  router bgp 1
    		address-family ipv4 unicast
    		neighbor 1.1.1.1
  switch(config)#
  switch(config)# configure replace bootflash:file verbose
  Collecting Running-Config
  Generating Rollback patch for switch profile
  Rollback Patch is Empty
  Note: Applying config parallelly may fail Rollback verification
  Collecting Running-Config
  #Generating Rollback Patch
  Executing Rollback Patch
  ========================================================
  config t
  feature bgp
  router bgp 1
  address-family ipv4 unicast
  neighbor 1.1.1.1
  ========================================================
  Generating Running-config for verification
  Generating Patch for verification
  
  Rollback completed successfully.
  
  switch(config)# sh run | section bgp
  feature bgp
  router bgp 1
    address-family ipv4 unicast
    neighbor 1.1.1.1
  
  Sample Example with ACL
  	switch(config)# configure replace bootflash:run_1.txt
  	Collecting Running-Config
  	Generating Rollback patch for switch profile
  	Rollback Patch is Empty
  	Note: Applying config parallelly may fail Rollback verification
  	Collecting Running-Config
  	#Generating Rollback Patch
  	Executing Rollback Patch
  	========================================================
  	config t
  	no ip access-list nexus-50-new-xyz
  	ip access-list nexus-50-new-xyz-jkl-abc
  	10 remark Newark
  	20 permit ip 17.31.5.0/28 any
  	30 permit ip 17.34.146.193/32 any
  	40 permit ip 17.128.199.0/27 any
  	50 permit ip 17.150.128.0/22 any
  	========================================================
  	Generating Running-config for verification
  	Generating Patch for verification
  
  	Rollback completed successfully.
  
  	switch(config)#
  
  
  	switch(config)# show run aclmgr | sec nexus-50-new-xyz-jkl-abc
  	ip access-list nexus-50-new-xyz-jkl-abc
    	10 remark Newark
   	 20 permit ip 17.31.5.0/28 any
    	30 permit ip 17.34.146.193/32 any
    	40 permit ip 17.128.199.0/27 any
    	50 permit ip 17.150.128.0/22 any

• Use the configure replace bootflash:user-config.cfg verify-only CLI command to generate and verify the patch semantically.

  switch(config)# configure replace bootflash:user-config.cfg verify-only         
  
  Version match between user file and running configuration.
  Pre-check for User config PASSED                          
  Collecting Running-Config                                 
  Converting to checkpoint file                             
  Generating Rollback Patch                                 
  Validating Patch                                          
  ========================================================  
  `config t `                                               
  `interface Ethernet1/1`                                   
  `shutdown`                                                
  `no switchport trunk allowed vlan`                        
  `no switchport mode`                                      
  `no switchport`                                           
  `exit`                                                    
  Skip non dme command for CR validation                    
  `interface Vlan1`                                         
  `shutdown`                                                
  `interface Ethernet1/1`                                   
  `shutdown`                                                
  `no switchport`                                           
  `ip address 1.1.1.1/24`                                   
  `exit`                                                    
  Skip non dme command for CR validation                    
  =============================================
  Patch validation completed successful                     
  switch(config)#      

• Use the configure replace bootflash:user-config.cfg best-effort verify-and-commit CLI command to replace the switch running configuration with the given user configuration after performing the sematic validation on patch.

  switch(config)# configure replace bootflash:user-config.cfg best-effort verify-and-commit 
          
   Version match between user file and running configuration.
  Pre-check for User config PASSED                          
  ADVISORY: Config Replace operation started...             
  Modifying running configuration from another VSH terminal in parallel
  is not recommended, as this may lead to Config Replace failure.      
  
  Collecting Running-Config
  Generating Rollback patch for switch profile
  Rollback Patch is Empty                     
  Collecting Running-Config                   
  Generating Rollback Patch                   
  
  Validating Patch
  Patch validation completed successful
  Executing Rollback Patch             
  During CR operation,will retain L3 configuration
  when vrf member change on interface             
  Generating Running-config for verification      
  Generating Rollback Patch                       
  
  Configure replace completed successfully. Please run 'show config-replace log exec' to see if there is any configuration that requires reload to take effect.
  
  switch(config)#
  

• Use the show config-replace log exec CLI command to check all the configuration that is executed and failures if any.

  switch(config)# show config-replace log exec 
  Operation            : Rollback to Checkpoint File
  Checkpoint file name : .replace_tmp_28081
  Scheme               : tmp
  Rollback done By     : admin
  Rollback mode        : atomic
  Verbose              : enabled
  Start Time           : Wed, 06:39:34 25 Jan 2017
  --------------------------------------------------------------------------------
  
  time: Wed, 06:39:47 25 Jan 2017
  Status: SUCCESS
  End Time             : Wed, 06:39:47 25 Jan 2017
  Rollback Status      : Success
  
  Executing Patch:
  ----------------
  switch#config t
  switch#no role name abc
  

• Use the show config-replace log verify CLI command to check the failed configuration if any.

  switch(config)# show config-replace log verify 
  Operation            : Rollback to Checkpoint File
  Checkpoint file name : .replace_tmp_28081
  Scheme               : tmp
  Rollback done By     : admin
  Rollback mode        : atomic
  Verbose              : enabled
  Start Time           : Wed, 06:39:34 25 Jan 2017
  End Time             : Wed, 06:39:47 25 Jan 2017
  Status               : Success
  
  Verification patch contains the following commands:
  ---------------------------------------------------
  !!                                                                  
  ! No changes
  --------------------------------------------------------------------------------
  
  time: Wed, 06:39:47 25 Jan 2017
  Status: SUCCESS
  

• Use the show config-replace status CLI command to check the status of configuration replace.

  switch(config)# show config-replace status 
  Last operation : Rollback to file
  Details:
    Rollback type: atomic replace_tmp_28081
    Start Time: Wed Jan 25 06:39:28 2017
    End Time: Wed Jan 25 06:39:47 2017
    Operation Status: Success
  switch(config)#