Modifying the Configuration for a Device

To configure a Juniper Networks device or to modify an existing configuration, you add statements to the configuration using the edit and set commands. For each statement hierarchy, you create the hierarchy starting with a statement at the top level and continuing with statements that move progressively lower in the hierarchy.

To modify the hierarchy, you use two configuration mode commands:

• edit—Moves to a specified hierarchy level. If that hierarchy level does not exist, the edit command creates it. The edit command has the following syntax:

• set—Creates a configuration statement and sets identifier values. After you issue a set command, you remain at the same level in the hierarchy. The set command has the following syntax:

  statement-path is the hierarchy to the configuration statement and the statement itself. If you have already moved to the statement’s hierarchy level, you can omit the statement path. statement is the configuration statement itself. identifier is a string that identifies an instance of a statement.

Statements can be either container statements or leaf statements. A container statement can include additional container statements within it, as well as leaf statements. A leaf statement, however, stands alone. The command edit? displays the container statements, while set? displays both the container and leaf statements, using > to differentiate between them.

The following example shows how to delete the ospf statement, effectively unconfiguring OSPF on the router:

Delete all statements from the current level down:

Unconfigure a specific property, in this case, removing the interface speed setting:

This example shows how you can create one virtual connection (VC) on an interface by copying an existing VC.

If you need to make changes to the configuration of a device, you can always remove the original configuration settings using the delete command and add your new configuration settings using the set command. However, there are other ways of modifying a configuration that are more efficient and easier to use.

This example shows how to use the following configuration mode commands to update an existing configuration:

• rename—Rename an existing configuration setting, such as an interface name. This can be useful when you are adding new interfaces to a device.

• copy—Copy a configuration setting and the entire hierarchy of statements configured under that setting. Copying configuration statements is useful when you are configuring many physical or logical interfaces of the same type.

• replace—Make global changes to text patterns in the configuration. For example, if you consistently misspell a word common to the description statement for all of the interfaces on your device, you can fix this mistake with a single command.

This example shows the use of the insert command.

Whereas a term added using the set command is placed at the end of the existing list of terms, you use the insert command to add a term in the order you specify. Specifying the order of statement is important in the cases in which the order of the statements matters because the configuration statements create a sequence that is analyzed in order.

As this example shows, you must create the term (or it must already exist), before you can place it using the insert command. The reference point for placing the term must also exist, for example, to place the term T1 before the term T2, both T1 and T2 must already exist, and be populated (Junos automatically removes empty terms).

This example shows a common use case in which the deactivate and activate configuration mode commands are used. It involves dual Routing Engines, primary and backup, that have graceful Routing Engine switchover (GRES) configured. The software on both Routing Engines needs to be upgraded. This can easily be accomplished by deactivating GRES, updating the Routing Engines, and then reactivating GRES.

You can make global changes to variables and identifiers in the device configuration by using the replace configuration mode command. This command replaces a pattern in a configuration with another pattern. For example, you can use this command to find and replace all occurrences of an interface name when a PIC is moved to another slot in the router.

pattern pattern1 is a text string or regular expression that defines the identifiers and values you want to replace in the configuration.

pattern2 is a text string or regular expression that replaces the identifiers and values located with pattern1.

Juniper Networks uses standard UNIX-style regular expression syntax (as defined in POSIX 1003.2). If the regular expression contains spaces, operators, or wildcard characters, enclose the expression in quotation marks. Greedy qualifiers (match as much as possible) are supported. Lazy qualifiers (match as little as possible) are not.

The upto n option specifies the number of objects replaced. The value of n controls the total number of objects that are replaced in the configuration (not the total number of times the pattern occurs). Objects at the same hierarchy level (siblings) are replaced first. Multiple occurrences of a pattern within a given object are considered a single replacement. For example, if a configuration contains a 010101 text string, the command replace pattern 01 with pattern 02 upto 2 replaces 010101 with 020202 (instead of 020201). Replacement of 010101 with 020202 is considered a single replacement (n = 1), not three separate replacements (n =3).

If you do not specify an upto option, all identifiers and values in the configuration that match pattern1 are replaced.

The replace command is available in configuration mode at any hierarchy level. All matches are case-sensitive.

The following table lists some replacement examples.

This example shows how you can use a backreference to replace a pattern.

This example shows how to replace an interface name globally in a configuration by using the replace command.

Using the replace command can be a faster and better way to change a configuration. For example, a PIC might be moved to another slot in a router, which changes the interface name. With one command you can update the whole configuration. Or you might want to quickly extend the configuration with other similar configurations, for example, similar interfaces.

By using a combination of the copy and replace commands, you can add to a configuration and then replace certain aspects of the newly copied configurations. The replace command works with regular expressions. Regular expressions are quick, flexible, and ubiquitous. You can fashion just about any pattern you might need to search for, and most programming languages support regular expressions.

Consider the hierarchy shown in Figure 1. The text string 010101 appears in three places: the description sections of ge-0/0/0, ge-0/0/0.0, and fe-0/0/1. These three instances are three objects. The following example shows how you can use the upto option to perform replacements in a device configuration:

Figure 1: Replacement by Object

An upto 2 option in the replace command converts 01 to 02 for two object instances. The objects under the main interfaces ge-0/0/0 and fe-0/0/1 will be replaced first (since these are siblings in the hierarchy level). Because of the upto 2 restriction, the replace command replaces patterns in the first and second instance in the hierarchy (siblings), but not the third instance (child of the first instance).

Adding comments to a device configuration makes the configuration file readable and more readily understood by users. You can include comments as you configure by using the annotate statement. In this example, comments are added by using the CLI for an already existing configuration: