Preconfiguring Physical Interfaces

This module describes the preconfiguration of physical interfaces.

Preconfiguration is supported for these types of interfaces and controllers:

  • Gigabit Ethernet

  • 10-Gigabit Ethernet

  • 100-Gigabit Ethernet

  • Management Ethernet

Preconfiguration allows you to configure line cards before they are inserted into the router. When the cards are inserted, they are instantly configured. The preconfiguration information is created in a different system database tree, rather than with the regularly configured interfaces. That database tree is known as the preconfiguration directory on the route processor.

There may be some preconfiguration data that cannot be verified unless the line card is present, because the verifiers themselves run only on the line card. Such preconfiguration data is verified when the line card is inserted and the verifiers are initiated. A configuration is rejected if errors are found when the configuration is copied from the preconfiguration area to the active area.


Note

One Gigabit Ethernet interface is not supported. Only physical interfaces can be preconfigured.


Note

From Cisco IOS XR Release 6.3.2, a six-seconds delay is introduced in error propagation from the driver to DPA for the MACSec line card and Oldcastle platforms. As a result, the BER algorithm on these platforms knows the error with a delay of 6 seconds.

Physical Interface Preconfiguration Overview

Preconfiguration is the process of configuring interfaces before they are present in the system. Preconfigured interfaces are not verified or applied until the actual interface with the matching location (rack/slot/module) is inserted into the router. When the anticipated line card is inserted and the interfaces are created, the precreated configuration information is verified and, if successful, immediately applied to the running configuration of the router.


Note

When you plug the anticipated line card in, make sure to verify any preconfiguration with the appropriate show commands.

Use the show run command to see interfaces that are in the preconfigured state.


Note

We recommend filling out preconfiguration information in your site planning guide, so that you can compare that anticipated configuration with the actual preconfigured interfaces when that line card is installed and the interfaces are up.


Tip

Tip Use the commit best-effort command to save the preconfiguration to the running configuration file. The commit best-effort command merges the target configuration with the running configuration and commits only valid configuration (best effort). Some configuration might fail due to semantic errors, but the valid configuration still comes up.

Prerequisites for Preconfiguring Physical Interfaces

Before preconfiguring physical interfaces, ensure that this condition is met:

  • Preconfiguration drivers and files are installed. Although it may be possible to preconfigure physical interfaces without a preconfiguration driver installed, the preconfiguration files are required to set the interface definition file on the router that supplies the strings for valid interface names.

Benefits of Interface Preconfiguration

Preconfigurations reduce downtime when you add new cards to the system. With preconfiguration, the new cards can be instantly configured and actively running during cards bootup.

Another advantage of performing a preconfiguration is that during a cards replacement, when the cards is removed, you can still see the previous configuration and make modifications.

How to Preconfigure Physical Interfaces

This task describes only the most basic preconfiguration of an interface.

SUMMARY STEPS

  1. configure
  2. interface preconfigure type interface-path-id
  3. Use one of the following commands:
    • ipv4 address ip-address subnet-mask
    • ipv4 address ip-address/ prefix
  4. Configure additional interface parameters, as described in this manual in the configuration chapter that applies to the type of interface that you are configuring.
  5. end or commit best-effort
  6. show running-config

DETAILED STEPS

Step 1

configure

Example:


 RP/0/RP0/CPU0:router#configure

Enters global configuration mode.

Step 2

interface preconfigure type interface-path-id

Example:


RP/0/RP0/CPU0:router(config)# interface preconfigure HundredGigE 0/3/0/2

Enters interface preconfiguration mode for an interface, where type specifies the supported interface type that you want to configure and interface-path-id specifies the location where the interface will be located in rack/slot/module/port notation.

Step 3

Use one of the following commands:

  • ipv4 address ip-address subnet-mask
  • ipv4 address ip-address/ prefix

Example:


RP/0/RP0/CPU0:router(config-if-pre)# ipv4 address 192.168.1.2/31

Assigns an IP address and mask to the interface.

Step 4

Configure additional interface parameters, as described in this manual in the configuration chapter that applies to the type of interface that you are configuring.

Step 5

end or commit best-effort

Example:


RP/0/RP0/CPU0:router(config-if-pre)# end

or 


RP/0/RP0/CPU0:router(config-if-pre)# commit

Saves configuration changes.

  • When you issue the end command, the system prompts you to commit changes: 
Uncommitted changes found, commit them before exiting (yes/no/cancel)?

  • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

  • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

  • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

  • Use the commit best-effort command to save the configuration changes to the running configuration file and remain within the configuration session. The commit best-effort command merges the target configuration with the running configuration and commits only valid changes (best effort). Some configuration changes might fail due to semantic errors.

Step 6

show running-config

Example:


RP/0/RP0/CPU0:router# show running-config

(Optional) Displays the configuration information currently running on the router.

Example

This example shows how to preconfigure a basic Ethernet interface: 


RP/0/RP0/CPU0:router# configure 
RP/0/RP0/CPU0:router(config)# interface preconfigure HundredGigE 0/0/1/0 
RP/0/RP0/CPU0:router(config-if)# ipv4 address 192.168.1.2/31 
RP/0/RP0/CPU0:router(config-if-pre)# commit

Information About Preconfiguring Physical Interfaces

To preconfigure interfaces, you must understand these concepts:

Use of the Interface Preconfigure Command

Interfaces that are not yet present in the system can be preconfigured with the interface preconfigure command in global configuration mode.

The interface preconfigure command places the router in interface configuration mode. Users should be able to add any possible interface commands. The verifiers registered for the preconfigured interfaces verify the configuration. The preconfiguration is complete when the user enters the end command, or any matching exit or global configuration mode command.


Note

It is possible that some configurations cannot be verified until the line card is inserted.

Do not enter the no shutdown command for new preconfigured interfaces, because the no form of this command removes the existing configuration, and there is no existing configuration.

Users are expected to provide names during preconfiguration that will match the name of the interface that will be created. If the interface names do not match, the preconfiguration cannot be applied when the interface is created. The interface names must begin with the interface type that is supported by the router and for which drivers have been installed. However, the slot, port, subinterface number, and channel interface number information cannot be validated.


Note

Specifying an interface name that already exists and is configured (or an abbreviated name like Hu0/3/0/0) is not permitted.