Cisco configuration file comments

The configuration commit auto-save command configures the system to save the running configuration to the specified file and location every time a commit command is run. Alternatively, you can save the configuration on a one-time basis by specifying the save-running keyword when you run the commit command.

Optional Locks the router configuration. The system configuration can be made only from the login terminal. If the configure command is entered without a keyword, the system is configured from the login terminal.

Configuration modes are used to enter changes to a target configuration session and commit those changes to the running configuration. From global configuration mode, you can enter any configuration mode. Configuration changes entered in global configuration mode impact the SDR to which the user is currently logged in. Use the configure command in administration EXEC mode to enter administration configuration mode and create a new target configuration.

From administration configuration mode, you can enter any administration configuration mode. Configuration changes entered in administration configuration mode can impact resources for the entire router.

See the command reference documentation for a specific command to determine the impact of commands entered in administration configuration mode. To lock the configuration so that no other user can commit changes to the running configuration during your configuration session, issue the configure command with the exclusive keyword. Changes to the target configuration remain inactive until the commit command is entered.

To leave global configuration or administration configuration mode and return to the EXEC or administration EXEC prompt, issue the end or exit command; you are prompted to commit any uncommitted changes. To leave configuration mode and return directly to EXEC or administration EXEC mode without being prompted to commit changes and without saving changes to the target configuration, enter the abort command in any configuration mode.

In the example, the configure command commits the configuration, and the end command terminates the configuration session and return the router to EXEC mode. The following example shows how to enter administration configuration mode and then configure an SDR. In this example, the user also enters SDR configuration mode.

To add a description to an interface configuration, use the description command in interface configuration mode. To remove the description, use the no form of this command. Use the description command to add a description to an interface configuration. The maximum number of characters is The following example shows how to add a description to an interface configuration. In this example, the description command names a Management Ethernet interface. To execute an EXEC mode command from a configuration mode, use the do command in any configuration mode.

To display the various EXEC mode commands that are available to execute with the do command, use the online help? The configure and describe commands are not supported with the do command. The following example shows how to execute an EXEC command from interface configuration mode. In this example, the do command displays output from the show protocols command within interface configuration mode:.

If you enter this command without committing the changes to the target configuration, you are prompted to do so:. If errors are found in the running configuration, the configuration session does not end.

To view the errors, enter the show configuration config command with the failed keyword. Entering Ctrl-Z is functionally equivalent to entering the end command. Use the abort command to exit the configuration session and return to EXEC or administration EXEC mode without being prompted to commit changes and without saving changes to the target configuration. The following example shows how to use the end command to end a configuration session.

Changes stored in the target configuration are committed by answering yes. To exit template configuration mode and return to global configuration mode, use the end-template command in template configuration mode.

Use the end-template command to exit template configuration mode after you have completed the template definition. To define a template, use the template command. To apply a template to the target configuration, use the apply-template command. To view the contents of a template, use the show running-config command with the optional template template-name keyword and argument.

To return the router to the next higher configuration mode, use the exit command in any configuration mode. When exiting from global or administration configuration mode to EXEC or administration EXEC mode, you are prompted to commit any uncommitted configuration changes.

Entering the exit command from global configuration is functionally equivalent to entering the end command. The following example shows how to return the router to the next higher command mode.

In this example, the exit command exits from interface configuration mode and returns to global configuration mode. The exit command is entered a second time to exit from global configuration mode and return to EXEC mode. Because the configuration has not been committed explicitly with the commit command , the system prompts to commit the configuration changes made during the session.

The following example shows how to use the exit command from EXEC mode to log off from a terminal session:. To specify or modify the hostname for the router, use the hostname command in global configuration mode. No blank or space characters are permitted as part of a name. Do not expect case to be preserved. Uppercase and lowercase characters look the same to many Internet software applications. It may seem appropriate to capitalize a name the same way you might do in English, but conventions dictate that computer names appear all lowercase.

To populate the target configuration with the contents of a previously saved configuration file, use the load command in global configuration or administration configuration mode. Storage device and directory path of the configuration file to be loaded into the target configuration. Use the load command to populate the target configuration with the contents of a previously saved configuration.

When loading a file, you must specify the device, directory path, and filename of the configuration file. Use the commit command in conjunction with the load command. Use the show configuration failed config command with the optional load keyword to display syntax errors that occurred during the last load operation.

The following example shows how to load a target configuration file into the current configuration session. The current configuration session is then populated with the contents of the file. To populate the target configuration with changes from previous configuration commits, use the load commit changes command in global configuration or administration configuration mode. Loads all configuration changes committed into the target buffer since and including a specific configuration commit, commit-id.

Loads the configuration changes into the target buffer that have been made during the last number of configuration commits specified with the number-of-commits argument. Use the load commit changes command to populate the target configuration with changes from previous configuration commits.

The changes are not applied until you enter the commit command. Use the show configuration config command to display the target configuration. The following example shows how to populate the target configuration with changes from a previous configuration commit:. To populate the target configuration with the contents of the previous failed configuration commit, use the load configuration failed command in global configuration or administration configuration mode.

Optional Loads the failed configurations from a previous router reload. Valid number-of-reloads values are 1 to 4.

Support was added for the previous number-of-reloads keyword and argument. Use the load configuration failed command to populate the target configuration with the contents of the previous failed configuration commit. The following example shows how to populate the target configuration with the contents of the previous failed configuration commit:.

To populate the target configuration with the contents of the previous removed configuration, use the load configuration removed command in global configuration or administration configuration mode. Use the load configuration removed command to populate the target configuration with the contents of the removed configuration during installation operations.

The following example shows how to populate the target configuration with the contents of the removed configuration during installation:. To populate the target configuration with the contents of a previous configuration, use the load rollback changes command in global configuration or administration configuration mode. Rolls back to the configuration that existed before the last number of commits specified with the number-of-commits argument were made. Rolls back to the running configuration that existed before the configuration specified with the commit-id argument.

Use the load rollback changes command to load rollback configuration changes to the target configuration. This command is similar to the rollback configuration command. The difference between the commands is that the load rollback changes command copies the rollback changes to the target configuration and does not commit the changes until the changes are explicitly committed with the commit command.

Use the show configuration rollback changes command to display rollback changes. The following example shows how to populate the target configuration with the contents of a previous configuration:.

To display manual pages, use the man command in EXEC mode. Displays the manual pages for a specific command. The command-name argument must include the complete command name. Displays all commands available in the feature. Use the man command with the feature keyword to list the available feature names. Displays a list of command names that match the keywords. Enter one or more keywords to match in a command. When entering multiple keywords, the keywords must be entered in the same sequential order as they are in the command.

You must have the documentation PIE installed before you can use the man command. If you attempt to run this command without the documentation PIE installed, an error is displayed as shown in the following example:. Use the man command to display the manual pages for a specific command on the basis of the command name, a feature, or a keyword. Each man page contains the command name, syntax, command mode, usage, examples, and related commands. The man command queries and displays command information about the router.

A query can be based on keywords or a feature. The feature feature-name keyword and argument display all commands that match the feature. For example, entering man feature c12k - base-1 displays all commands that match the c12k -base-1 feature.

The keyword keywords keyword and argument display all commands that contain the specified keyword. For example, man keyword ipv4 displays all commands that contain ipv4. The following example shows how to display the manual page for the arp timeout command:. File system location of the file to be displayed. Include the file system alias for the filesystem argument, followed by a colon, and the directory path of the file to be displayed. Optional Begins unfiltered output of the more command with the first line that contains the regular expression.

Use the more command to display any text file, especially an ASCII file stored on the router or accessible through the network. The file can be a configuration file or any other text file. Begins unfiltered output of the more command with the first line that contains the regular expression. You can also specify a filter at the --More-- prompt of a more command output.

The filter remains active until the command output finishes or is interrupted using Ctrl-Z or Ctrl-C. After you specify a filter for a more command, you cannot specify another filter at the next --More-- prompt. The first specified filter remains until the more begin command output finishes or until you interrupt the output. The use of the keyword does not constitute a filter.

The following example shows partial sample output from the more command. The output displays a configuration file saved on the hard disk drive. The following example shows partial sample output of the more command on the sample file config. The command usage is more disk0:config. To display the current configuration submode from a configuration submode, use the pwd command in any supported configuration submode.

The following example shows how to use the pwd command from an interface configuration submode:. Optional Assigns a text label to this rollback. The label argument must begin with a letter.

Optional Assigns a text comment to this rollback. The comment argument can be up to 60 characters long. Each time the commit command is entered, a commit ID is assigned to the new configuration.

You can revert the system to the configuration of a previous commit ID with the rollback configuration command:. Use the force keyword to override commits that would fail otherwise.

This is useful in the event of a low-memory condition on the router, to revert to a commit that would remove a configuration that caused the low-memory condition. The rollback operation may fail if you try to rollback two or more commits where the individual commits involve the configuration and removing of the configuration of the same item, and there is a dependency of one item over another in any of the individual commit operations.

The following example shows how to roll back to a specific commit ID. In this example, the show configuration commit list command displays the available rollback points.

The configuration is then rolled back to a prior commit with the rollback configuration command. The following example shows how to roll back to the configuration that existed prior to the last two configuration commits:. To return to configuration mode from a configuration submode, use the root command in any supported configuration submode.

The following example shows how to use the root command to return to configuration mode from the interface configuration submode:. The following example shows how to use the root command from a submode configurable under the template submode. In this example, the root command is used to return to configuration mode from the username submode:.

The root command is not available from the template submode, but is available in the submodes configurable under the template submode.

To save the contents of a configuration to a file, use the save configuration command in global configuration or administration configuration mode. To save a configuration to a file, use the save configuration command. To save a configuration that failed to a file, use the save configuration failed command. To save the changes of a configuration to a file, use the save configuration changes command in global configuration or administration configuration mode.

To save the configuration changes to be made during a replace operation to a file, use the save configuration changes command. To save the changes for a commit, or a series of commits, to a file, use the save configuration commit changes command in global configuration or administration configuration mode. Saves changes made in the most recent number-of-commits. Saves changes made since and including a specific commit-id. Use the command to save the changes made in a commit operation to a file.

You can specify a specific commit ID, all the changes since a specified commit ID, or the changes that occurred during the last n commits. To save the contents of the failed configuration, use the save configuration failed command in global configuration or administration configuration mode.

Optional Saves a failed startup configuration from the specified previous sessions. The number argument is a value between 1 and 4 that indicates how many failed startup configurations to save. The startup keyword was added in administration configuration mode. To save a configuration that failed during startup to a file, use the command with the startup keyword. To save the contents of a merged configuration to a file, use the save configuration merge command in global configuration or administration configuration mode.

To save the contents of a removed configuration to a file, use the save configuration removed command in global configuration or administration configuration mode. When a package is deactivated, the configuration belonging to that package is removed from the running configuration and saved to a file. To save a copy of the removed configuration file, use the save configuration removed command.

To view a list of the available removed configuration files, use the save configuration removed command followed by a question mark:. Displays changes that would be made by the rollback configuration command or displays the list of commit IDs. To save the rollback changes, use the save rollback changes command in global configuration or administration configuration mode. Saves rollback changes up to a specific commit-id.

Use the save rollback changes command to save the changes that would be made in a configuration rollback to a specific commit point or for a series of commits. The following example shows that the rollback changes for the commit point 5 are saved to the file sample4 on disk Use the command to set the default AFI for the current session. This command acts as a keystroke shortcut for show commands. If the default AFI setting is set to IPv4, then you would not have to specify the ipv4 keyword for show commands that support the ipv4 keyword.

Use the show default-afi-safi-vrf command to display the default AFI setting. Use the command to set the default SAFI setting for the current session. If the default SAFI setting is set to unicast, you would not have to specify the unicast keyword for show commands that support that keyword.

For example, if the default SAFI setting is set to unicast, you could issue the show router command without specifying the unicast keyword to display information about unicast address prefixes in the Routing Information Base RIB. Use the show default-afi-safi-vrf command to display the default SAFI setting. Use the set default-vrf command to set the default VRF setting for the current session. Use the show default-afi-safi-vrf command to display the default VRF setting. In the following command, the show route command is entered without specifying a VRF name.

In the following example, the default VRF is set to empty and the show route command displays the system default VRF information:.

To display information about the system configuration or operational state, use the show command in EXEC mode, administration EXEC mode, or any configuration mode.

Optional Regular expression found in show command output. Optional Begins unfiltered output of the show command with the first line that contains the regular expression. Optional Writes the output lines that contain the regular expression to the specified file on the specified file system. Include the file system alias for the filesystem argument, followed by a colon, and the directory path and filename.

The show commands display information about the system and its configuration. To display a list of the available show commands, use the question mark? Begins unfiltered output of the show command command with the first line that contains the regular expression. Writes the output lines that contain the regular expression to the specified file on the specified file system.

You can also specify a filter at the --More-- prompt of a show command output. Task ID for the feature used with the show command. For example, the show interfaces command requires read privileges in the interface task ID.

The following example shows output from the show interface include protocol command. On most systems, the Ctrl-Z key combination can be entered at any time to interrupt the output and return to EXEC mode.

For example, use the show running-config begin hostname command to start the display of the running configuration file at the line containing the hostname setting, then use Ctrl-Z when you get to the end of the information you are interested in. The following example shows sample output from the show configuration running begin line command. The use of the begin keyword does not constitute a filter. To display all defined aliases or the aliases defined in a specified mode, use the show aliases command in EXEC mode.

Use the show aliases command to display all aliases currently configured on the system. The following example illustrates sample output from the show aliases command. The output displays a summary of all the command aliases configured. To display information about the current configuration session target configuration , use the show configuration command in any configuration mode.

Optional Displays the configuration that occurs if the contents of the uncommitted changed target configuration are committed to the running configuration.

When the show configuration command is entered without an argument, the uncommitted changes to the target configuration are displayed. Use the show configuration command to display details on uncommitted configuration changes.

Use the show configuration command with the running keyword to display the running active configuration. Prior to committing the target configuration, use the show configuration command with the merge keyword from any configuration mode to display the result of merging the target configuration with the running configuration. In this example, the show configuration command displays uncommitted changes made during a configuration session:. The following example shows sample output from the show configuration command with the optional merge keyword.

The command is entered during a configuration session. The output displays the result of merging the target and running configuration, without committing the changes. To display the configuration changes to be made during a replace operation, use the show configuration changes command in global configuration or administration configuration mode. To display the changes made to the running configuration by previous configuration commits, a configuration commit, or for a range of configuration commits, use the show configuration commit changes command in EXEC, administration EXEC, administration configuration, or global configuration mode.

Displays all changes committed to the running configuration since and including a specific configuration commit.

Displays the changes made to the running configuration during the last number of configuration commits specified for the number-of-commits argument. Each time a configuration is committed with the commit command, the configuration commit operation is assigned a commit ID. The show configuration commit changes command displays the configuration changes made since the specified commit. To display a list of the available commit IDs, enter the show configuration commit list command.

You can also display the commit IDs by entering the show configuration commit changes command with the online help function? The following example shows sample output from the show configuration commit changes command. The output displays commit IDs. The following example shows sample output from the show configuration commit changes command with the commit-id argument.

In this example, the output displays the changes made in the configuration commit assigned commit ID The following example shows sample output from the show configuration commit changes command with the since commit-id keyword and argument. In this example, the output displays the configuration changes made since the configuration commit assigned commit ID was committed. The following example shows sample output from the show configuration commit changes command with the diff keyword.

In the display, the following symbols signify changes:. To display information about the configuration commits stored in the commit database, use the show configuration commit list command in EXEC, administration EXEC, administration configuration, or global configuration mode. Optional Number of commits beginning with the most recent commit that are available for rollback.

If this command is entered without any optional arguments or keywords, the output displays information about all the configuration commits stored in the commit database. This command replaced the show rollback points command, which was available in previous releases. Use the show configuration commit list command to list the commit IDs up to that are available for rollback. The following example shows sample output from the show configuration commit list command. The output displays the commit IDs that are available for rollback.

Table 1 describes the significant fields shown in the display. If a label was assigned to a commit, the first 10 characters of the label display; otherwise, the autogenerated commit ID displays.

To maintain a configuration file that exceeds the size of NVRAM, perform the tasks described in the following sections:. If you try to load a configuration that is more than three times larger than the NVRAM size, the following error message is displayed:. When you have finished changing the running-configuration, save the new configuration. To store the startup configuration in flash memory, complete the tasks in this section:.

Copies the current startup configuration to the new location to create the configuration file. To use a network server to store large configurations, complete the tasks in this section:. Specifies that the startup configuration file be loaded from the network server at startup. To copy a configuration file from flash memory directly to your startup configuration in NVRAM or your running configuration, enter one of the commands in Step The following example copies the file named ios-upgrade-1 from partition 4 of the flash memory PC Card in usbflash0 to the device startup configurations:.

On platforms with multiple flash memory file systems, you can copy files from one flash memory file system, such as internal flash memory to another flash memory file system. Copying files to different flash memory file systems lets you create backup copies of working configurations and duplicate configurations for other devices.

To copy a configuration file between flash memory file systems, use the following commands in EXEC mode:. The source device and the destination device cannot be the same. For example, the copy usbflash0: usbflash0: command is invalid. The following example copies the file named running-config from partition 1 on internal flash memory to partition 1 of usbflash0 on a device.

In this example, the source partition is not specified, so the device prompts for the partition number:. To copy a configuration file from an FTP server to a flash memory device, complete the task in this section:. Optional Enters global configuration mode. Optional Exits configuration mode. This step is required only if you override the default remote username see Steps 3 and 4. Copies the configuration file from a network server to the flash memory device using FTP.

To copy a configuration file from an RCP server to a flash memory device, complete the tasks in this section:. This step is required only if you override the default remote username or password see Step 3. Copies the configuration file from a network server to the flash memory device using RCP. Respond to any device prompts for additional information or confirmation. Prompting depends on how much information you provide in the copy command and the current setting of the file prompt command.

To copy a configuration file from a TFTP server to a flash memory device, complete the tasks in this section:. Copies the file from a TFTP server to the flash memory device.

Reply to any device prompts for additional information or confirmation. The following example shows the copying of the configuration file named switch-config from a TFTP server to the flash memory card inserted in usbflash0. The copied file is renamed new-config. To re-execute the commands located in the startup configuration file, complete the task in this section:. You can clear the configuration information from the startup configuration.

If you reboot the device with no startup configuration, the device enters the Setup command facility so that you can configure the device from scratch. To clear the contents of your startup configuration, complete the task in this section:. The startup configuration file cannot be restored once it has been deleted. This feature allows you to recover a deleted file. To delete a specified configuration on a specific flash device, complete the task in this section:.

On Class A and B Flash file systems, when you delete a specific file in flash memory, the system marks the file as deleted, allowing you to later recover a deleted file using the undelete EXEC command.

Erased files cannot be recovered. To permanently erase the configuration file, use the squeeze EXEC command. On Class C Flash file systems, you cannot recover a file that has been deleted. Copies the configuration file to the flash file system from which the device loads the file on restart. The following example copies the running configuration file to the device. This configuration is then used as the startup configuration when the system is restarted:.

After you specify a location for the startup configuration file, the nvram:startup-config command is aliased to the new location of the startup configuration file. The more nvram:startup-config EXEC command displays the startup configuration, regardless of its location.

A distilled version is one that does not contain access list information. If NVRAM contains a complete configuration file, the device prompts you to confirm your overwrite of the complete version with the distilled version.

Eventually, Flash memory fills up as the old configuration files still take up memory. Use the squeeze EXEC command to permanently delete the old configuration files and reclaim the space. You can specify an ordered list of network configuration and host configuration filenames. To configure the device to download configuration files at system startup, perform at least one of the tasks described in the following sections:.

If the device 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 device displays the following message on the console terminal:. If there are any problems with the startup configuration file, or if the configuration register is set to ignore NVRAM, the device enters the Setup command facility. To configure the Cisco IOS software to download a network configuration file from a server at startup, complete the tasks in this section:. If you do not specify a network configuration filename, the Cisco IOS software uses the default filename network-confg.

If you omit the address, the device uses the broadcast address. You can specify more than one network configuration file. The software tries them in order entered until it loads one. This procedure can be useful for keeping files with different configuration information loaded on a network server.

To configure the Cisco IOS software to download a host configuration file from a server at startup, complete the tasks in this section:.

You can specify more than one host configuration file. The Cisco IOS software tries them in order entered until it loads one. In the following example, a device is configured to download the host configuration file named hostfile1 and the network configuration file named networkfile1.

The device uses TFTP and the broadcast address to obtain the file:. This table provides release and related information for features explained in this module.

These features are available on all releases subsequent to the one they were introduced in, unless noted otherwise. Use Cisco Feature Navigator to find information about platform and software image support. Skip to content Skip to search Skip to footer. Book Contents Book Contents. Find Matches in This Book. PDF - Complete Book 5. Updated: December 16, Chapter: Managing Configuration Files. Restrictions for Managing Configuration Files Many of the Cisco IOS commands described in this document are available and function only in certain configuration modes on the device.

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]?

You may want to perform this function for one of the following reasons: To restore a backed-up configuration file. When you copy a configuration file from the device to a server using RCP, the Cisco IOS software sends the first valid username it encounters in the following sequence: The username specified in the copy EXEC command, if a username is specified.

The device host name. For example, suppose the device contains the following configuration lines: hostname Device1 ip rcmd remote-username User0 If the device IP address translates to device1.

Refer to the documentation for your RCP server for more information. When you copy a configuration file from the device to a server using FTP, the Cisco IOS software sends the first valid username it encounters in the following sequence: The username specified in the copy EXEC command, if a username is specified.

The device sends the first valid password it encounters in the following sequence: The password specified in the copy command, if a password is specified. Refer to the documentation for your FTP server for more information. Example The following example shows how to copy files through a VRF, using the copy command: Device Address or name of remote host [ Source username [ScpUser]?

After the configurations are copied, to save your configurations, use write memory command and then either reload the switch or run the copy startup-config running-config command Configuration Files Larger than NVRAM To maintain a configuration file that exceeds the size of NVRAM, you should be aware of the information in the following sections.

Configuring the Device to Download Configuration Files You can configure the device to load one or two configuration files at system startup. Enter your password if prompted. Step 3 more file-url Example: Device more Step 4 show running-config Example: Device show running-config Displays the contents of the running configuration file. Step 5 show startup-config Example: Device show startup-config Displays the contents of the startup configuration file.

Step 2 configure terminal Example: Device configure terminal Enters global configuration mode. Step 3 configuration command Example: Device config configuration command Enter the necessary configuration commands.

Step 5 copy system:running-config nvram:startup-config Example: Device copy system:running-config nvram:startup-config Saves the running configuration file as the startup configuration file. Examples In the following example, the device prompt name of the device is configured. Device configure terminal Device config! The following command provides the switch host name. Step 3 ip rcmd remote-username username Example: Device config ip rcmd remote-username NetAdmin1 Optional Changes the default remote username.

Step 4 end Example: Device config end Optional Exits global configuration mode. Write file start-confg on host Step 2 configure terminal Example: Device configure terminal Enters global configuration mode on the device.

Step 3 ip ftp username username Example: Device config ip ftp username NetAdmin1 Optional Specifies the default remote username. Step 4 ip ftp password password Example: Device config ip ftp password adminpassword Optional Specifies the default password.

Step 5 end Example: Device config end Optional Exits global configuration mode. Examples In the following example, the software is configured from the file named tokyo-confg at IP address Step 2 configure terminal Example: Device configure terminal Optional Enters configuration mode from the terminal. Step 3 ip rcmd remote-username username Example: Device config ip rcmd remote-username NetAdmin1 Optional Specifies the remote username.

Step 2 configure terminal Example: Device configure terminal Optional Allows you to enter global configuration mode. Step 3 service compress-config Example: Device config service compress-config Specifies that the configuration file be compressed. Step 4 end Example: Device config end Exits global configuration mode.

Step 2 copy nvram:startup-config flash-filesystem:filename Example: Device copy nvram:startup-config usbflash0:switch-config Copies the current startup configuration to the new location to create the configuration file. Step 3 configure terminal Example: Device configure terminal Enters global configuration mode.

Step 5 end Example: Device config end Exits global configuration mode. Step 7 copy system:running-config nvram:startup-config Example: Device config copy system:running-config nvram:startup-config When you have finished changing the running-configuration, save the new configuration.

Step 5 service config Example: Device config service config Enables the switch to download configuration files at system startup. As mentioned previously, these comments are not preserved after a 'write mem' But, they will not destroy your configuration script if pasted into a configuration prompt. Each line, that begins with "! It is not necessary to begin the line with "! It was also said, that comment line will be filtered out when loading the configuration file on the device.

Shows up in running config and is saved to startup config when you reboot or login its the first thing you'll see. You can't leave a comment directly in the running-config, but you can absolutely leave a "description" on interfaces that can be seen in the running-config. Here is a copy of my output from a Catalyst Abridged :. Enter configuration commands, one per line.

SW-4 config int vlan SW-4 config-if description? LINE Up to characters describing this interface. SW-4 config-if do show run. Interface descriptions are often used for monitoring systems, a sort of self documenting. Remember you can also use "name" on a static route to give other engineers a clue when troubleshooting.