Configuration files contain the Cisco IOS software commands used to customize the functionality of your Cisco routing device (router, access server, switch, and so on). Commands are parsed (translated and executed) by the Cisco IOS software when the system is booted (from the startup-config file) or when you enter commands at the CLI in a configuration mode.

Startup configuration files (startup-config) are used during system startup to configure the software. Running configuration files (running-config) contain the current configuration of the software. The two configuration files can be different. For example, you may want to change the configuration for a short time period rather than permanently. In this case, you would change the running configuration using the configureterminal EXEC command but not save the configuration using the copyrunning-configstartup-config EXEC command.

To change the running configuration, use the configureterminal command, as described in the "Modifying the Configuration File at the CLI " section. As you use the Cisco IOS configuration modes, commands generally are executed immediately and are saved to the running configuration file either immediately after you enter them or when you exit a configuration mode.

To change the startup configuration file, you can either save the running configuration file to the startup configuration using the copyrunning-configstartup-config EXEC command or copy a configuration file from a file server to the startup configuration (see the "Copying a Configuration File from a TFTP Server to the Router " section for more information).

To enter configuration mode on the router, enter the configurecommand at the privileged EXEC prompt. The Cisco IOS software responds with the following prompt asking you to specify the terminal, memory, or a file stored on a network server (network) as the source of configuration commands:

Configuring from terminal, memory, or network [terminal]?

Configuring from the terminal allows you to enter configuration commands at the command line, as described in the following section. Configuring from memory loads the startup configuration file. See the "Reexecuting the Configuration Commands in the Startup Configuration File " section for more information. Configuring from the network allows you to load and execute configuration commands over the network. See the "Copying a Configuration File from a TFTP Server to the Router " section for more information.

The Cisco IOS software accepts one configuration command per line. You can enter as many configuration commands as you want. You can add comments to a configuration file describing the commands you have entered. Precede a comment with an exclamation point ( !). Because comments are not stored in NVRAM or in the active copy of the configuration file, comments do not appear when you list the active configuration with theshowrunning-configormoresystem:running-config EXEC command. Comments do not display when you list the startup configuration with the showstartup-config or morenvram:startup-config EXEC mode command. Comments are stripped out of the configuration file when it is loaded onto the router. However, you can list the comments in configuration files stored on a File Transfer Protocol (FTP), remote copy protocol (rcp), or Trivial File Transfer Protocol (TFTP) server. When you configure the software using the CLI, the software executes the commands as you enter them.

Configuration files are stored in the following locations:

• The running configuration is stored in RAM.
• On all platforms except the Class A Flash file system platforms, the startup configuration is stored in nonvolatile random-access memory (NVRAM).
• On Class A Flash file system platforms, the startup configuration is stored in the location specified by the CONFIG_FILE environment variable (see the "Specifying the CONFIG_FILE Environment Variable on Class A Flash File Systems" section). The CONFIG_FILE variable defaults to NVRAM and can be a file in the following file systems:
  • nvram: (NVRAM)
  • bootflash: (internal Flash memory)
  • slot0: (first PCMCIA slot)
  • slot1: (second PCMCIA slot)

You can copy configuration files from a TFTP, rcp, or FTP server to the running configuration or startup configuration of the router. You may want to perform this function for one of the following reasons:

• To restore a backed-up configuration file.
• To use the configuration file for another router. For example, you may add another router to your network and want it to have a similar configuration to the original router. By copying the file to the new router, you can change the relevant parts rather than re-creating the whole file.
• To load the same configuration commands on to all the routers in your network so that all the routers have similar configurations.

The copy{ftp: | rcp: | tftp:system:running-configEXECcommand loads the configuration files into the router as if you were typing the commands in at the command line. The router does not erase the existing running configuration before adding the commands. If a command in the copied configuration file replaces a command in the existing configuration file, the existing command will be erased. For example, if the copied configuration file contains a different IP address in a particular command than the existing configuration, the IP address in the copied configuration will be used. However, some commands in the existing configuration may not be replaced or negated. In this case, the resulting configuration file will be a mixture of the existing configuration file and the copied configuration file, with the copied configuration file having precedence.

In order to restore a configuration file to an exact copy of a file stored on a server, you need to copy the configuration file directly to the startup configuration (using the copyftp:| rcp:| tftp:} nvram:startup-configcommand) and reload the router.

To copy configuration files from a server to a router, perform the tasks described in the following sections:

The protocol you use depends on which type of server you are using. The FTP and rcp transport mechanisms provide faster performance and more reliable delivery of data than TFTP. These improvements are possible because the FTP and rcp transport mechanisms are built on and use the TCP/IP stack, which is connection-oriented.

• Copy a Configuration File from the Router to a TFTP Server
  
• Copy a Configuration File from the Router to an rcp Server
  
• Copy a Configuration File from the Router to an FTP Server
  

To maintain a configuration file that exceeds size of NVRAM, you should be aware of the information in the following sections:

• Compressing the Configuration File
  
• Storing the Configuration in Flash Memory on Class A Flash File Systems
  
• Loading the Configuration Commands from the Network
  

The Cisco IOS command-line parser in the Cisco IOS software performs the translation and execution (parsing) of command lines. The Parser Cache feature was developed to rapidly process large configuration files, thereby dramatically improving load time.

The Parser Cache feature allows the rapid recognition and translation of configuration lines in a configuration file that differ slightly from previously used configuration lines (for example, pvc 0/100, pvc 0/101, and so on) by dynamically creating, caching, and reusing simplified parse graphs. This improvement is useful primarily for configuration files that repeat similar commands hundreds or thousands of times, such as cases in which thousands of virtual circuits must be configured for subinterfaces, or hundreds of access lists must be configured. Performance will improve the most for those files in which the same commands are used repeatedly but the numerical arguments change from command to command.

The Parser Cache is enabled by default on all platforms using Cisco IOS Release 12.1(5)T and later releases. However, users with Cisco devices that do not require large configuration files may want to disable the Parser Cache to free the resources used by this feature. (Memory used by this feature depends on the size of the configuration files parsed, but is generally less than 512 KB.)

There are several ways to control the parser cache (these are all optional):

• Clearing the Parser Cache--To free resources or to reset the parser cache memory, you may wish to clear the parse entries and hit/miss statistics stored by the Parser Cache feature
• Disabling the Parser Cache--The Parser Cache feature is enabled by default. To disable the Parser Cache feature, use the no parser cache command in global configuration mode. When the parser cache is disabled, the noparsercache command line is written to the running configuration file. If you wish to disable the parser cache to free system resources, you should clear the parser cache before issuing the noparsercache command. You will not be able to clear the parser cache after disabling it.
• Reenabling the Parser Cache--To reenable the Parser Cache feature after disabling it, use the parsercache command in global configuration mode
• Monitoring the Parser--Statistics about the last configuration file parsed are kept in the system memory, along with hit/miss statistics on the commands parsed by the Parser Cache feature. "Hits" and "misses" refer to the matches that the parser cache was able to make to similar commands used previously in the configuration session. Those commands that are matched ("hits") be parsed more efficiently. The parser cache cannot improve the parse time for those commands it was unable to match ("misses").

You can configure the router to load one or two configuration files at system startup. The configuration files are loaded into memory and read in as if you were typing the commands at the command line. Thus, the configuration for the router will be a mixture of the original startup configuration and the one or two downloaded configuration files.

• Network Versus Host Configuration Files
  

1.    enable

2.    show bootvar

3.    more file-url

4.    show running-config

5.    show startup-config

1.    enable

2.    configure terminal

3.    configuration command

4.   Do one of the following:

5.    copy system:running-config nvram:startup-config

Examples

In the following example, the router prompt name of the router is configured. The comment line, indicated by the exclamation mark (!), does not execute any command. The hostname command is used to change the router name from Router to new_name. By pressing Ctrl-Z (^Z) or entering the endcommand, the user quits configuration mode. The copysystem:running-confignvram:startup-config command saves the current configuration to the startup configuration.

Router# configure terminal
Router(config)# !The following command provides the router host name.
Router(config)# hostname new_name
new_name(config)# end
new_name# copy system:running-config nvram:startup-config

When the startup configuration is NVRAM, it stores the current configuration information in text format as configuration commands, recording only nondefault settings. The memory is checksummed to guard against corrupted data.

Note	Some specific commands might not get saved to NVRAM. You will need to enter these commands again if you reboot the machine. These commands are noted in the documentation. We recommend that you keep a list of these settings so that you can quickly reconfigure your router after rebooting.

1.    enable

2.    copy system:running-config tftp: [[[//location ]/directory ]/filename ]

3.    copy nvram:startup-config tftp: [[[//location ]/directory ]/filename ]

Tokyo# copy system:running-config tftp://172.16.2.155/tokyo-confg
Write file tokyo-confg on host 172.16.2.155? [confirm] y
Writing tokyo-confg!!! [OK]

• What to Do Next
  

1.    enable

2.    configure terminal

3.    ip rcmd remote-username username

4.    end

5.   Do one of the following:

• Examples
  
• What to Do Next
  

1.    enable

2.    configure terminal

3.    ip ftp username username

4.    ip ftp password password

5.    end

6.   Do one of the following:

• Examples
  
• What to Do Next
  

1.    enable

2.    copy tftp: [[[//location ]/directory ]/filename ] system:running-config

3.    copy tftp: [[[//location ]/directory ]/filename ] nvram:startup-config

Router1# copy tftp://172.16.2.155/tokyo-confg system:running-config
 
Configure using tokyo-confg from 172.16.2.155? [confirm] y
 
Booting tokyo-confg from 172.16.2.155:!!! [OK - 874/16000 bytes]

• What to Do Next
  

1.    enable

2.    configure terminal

3.    ip rcmd remote-username username

4.    end

5.    copy rcp: [[[//[username@]location ]/directory ]/filename ]system:running-config

• Examples
  
• What to Do Next
  

1.    enable

2.    configure terminal

3.    ip ftp username username

4.    ip ftp password password

5.    end

6.    copy ftp: [[[//[username [:password ]@]location ]/directory ]/filename ]system:running-config

• Examples
  
• What to Do Next
  

To maintain a configuration file that exceeds size of NVRAM, perform the tasks described in the following sections:

• Compressing the Configuration File
  
• Storing the Configuration in Flash Memory on Class A Flash File Systems
  
• Loading the Configuration Commands from the Network
  

To control the Parser Cache feature, perform the tasks described in the following sections. All of these tasks are optional:

• Clearing the Parser Cache
  
• Disabling the Parser Cache
  
• Reenabling the Parser Cache
  
• What to Do Next
  

1.    enable

2.   Do one of the following:

Router# copy slot0:4:ios-upgrade-1 nvram:startup-config
 
Copy '
ios-upgrade-1
' from flash device
  as 'startup-config' ? [yes/no] yes
 
[OK]

1.    enable

2.    show source-filesystem :

3.    copy source-filesystem : [partition-number:][filename ] dest-filesystem:[partition-number:][filename ]

4.    verify dest-filesystem : [partition-number:][filename ]

Router# copy flash: slot1:
 
System flash
Partition   Size    Used      Free      Bank-Size  State          Copy Mode
  1         4096K   3070K     1025K     4096K      Read/Write     Direct
  2        16384K   1671K    14712K     8192K      Read/Write     Direct
[Type ?<no> for partition directory; ? for full directory; q to abort]
Which partition? [default = 1] 
System flash directory, partition 1:
File  Length   Name/status
  1   3142748  dirt/network/mars-test/c3600-j-mz.latest  
  2   850      running-config  
[3143728 bytes used, 1050576 available, 4194304 total]
PCMCIA Slot1 flash directory:
File  Length   Name/status
  1   1711088  dirt/gate/c3600-i-mz 
  2   850      running-config 
[1712068 bytes used, 2482236 available, 4194304 total]
Source file name? running-config
 
Destination file name [running-config]? 
Verifying checksum for 'running-config' (file # 2)...  OK
Erase flash device before writing? [confirm]
Flash contains files. Are you sure you want to erase? [confirm]
Copy 'running-config' from flash: device
  as 'running-config' into slot1: device WITH erase? [yes/no] yes
 
Erasing device... eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee ...erased
!
 [OK - 850/4194304 bytes]
Flash device copy took 00:00:30 [hh:mm:ss]
Verifying checksum...  OK (0x16)

1.    enable

2.    configure terminal

3.    ip ftp username username

4.    ip ftp password password

5.    end

6.    copy ftp: [[[//[username:password@]location ]/directory ]/filename ] flash-filesystem:[partition-number:][filename ]

• What to Do Next
  

1.    enable

2.    configure terminal

3.    ip rcmd remote-username username

4.    end

5.    copy rcp: [[[//[username@]location ]/directory ]/filename ] flash-filesystem:[partition-number:][filename ]

1.    enable

2.    copy tftp: [[[//location ]/directory ]/filename ] flash-filesystem:[partition-number:][filename ]

Router# copy tftp:router-config slot0:new-config

1.    enable

2.    configure memory

1.    enable

2.    erase nvram

1.    enable

2.    delete flash-filesystem : filename

1.    enable

2.    copy [flash-url| ftp-url | rcp-url| tftp-url | system:running-config | nvram:startup-config] dest-flash-url

3.    configure terminal

4.    boot config dest-flash-url

5.    end

6.    copy system:running-config nvram:startup-config

7.    show bootvar

Router# copy system:running-config slot0:config2
Router# configure terminal
Router(config)# boot config slot0:config2
Router(config)# end
Router# copy system:running-config nvram:startup-config
[ok]
Router# show bootvar
BOOT variable = slot0:rsp-boot-m
CONFIG_FILE variable = nvram:
Current CONFIG_FILE variable = slot0:config2
Configuration register is 0x010F

• What to Do Next
  

You can specify an ordered list of network configuration and host configuration filenames. The Cisco IOS XE software scans this list until it loads the appropriate network or host configuration file.

To configure the router to download configuration files at system startup, perform at least one of the tasks described in the following sections:

• "Configuring the Router to Download the Network Configuration File"
• "Configuring the Router to Download the Host Configuration File"

If the router fails to load a configuration file during startup, it tries again every 10 minutes (the default setting) until a host provides the requested files. With each failed attempt, the router displays the following message on the console terminal:

Booting host-confg... [timed out]

If there are any problems with the startup configuration file, or if the configuration register is set to ignore NVRAM, the router enters the Setup command facility.

• Configuring the Router to Download the Network Configuration File
  
• Configuring the Router to Download the Host Configuration File