is-level

Function

The is-level command configures a level for an IS-IS device.

The undo is-level command restores the default value.

By default, the level of an IS-IS device is Level-1-2.

Format

is-level { level-1 | level-1-2 | level-2 }

undo is-level

Parameters

Parameter	Description	Value
level-1	Sets the level of the device to Level-1. It calculates only intra-area routes and maintains the LSDBs of Level-1.	-
level-1-2	Sets the level of the device to Level-1-2. It calculates both Level-1 and Level-2 routes and maintains the LSDBs of Level-1 and Level-2.	-
level-2	Sets the level of the device to Level-2. It calculates Level-2 routes and maintains the LSDBs of Level-2.	-

Parameter

Description

Value

level-1

Sets the level of the device to Level-1. It calculates only intra-area routes and maintains the LSDBs of Level-1.

level-1-2

Sets the level of the device to Level-1-2. It calculates both Level-1 and Level-2 routes and maintains the LSDBs of Level-1 and Level-2.

level-2

Sets the level of the device to Level-2. It calculates Level-2 routes and maintains the LSDBs of Level-2.

Views

IS-IS view

Default Level

2: Configuration level

Task Name and Operations

Task Name	Operations
isis	write

Usage Guidelines

Usage Scenario

To support a network with a large number of routes, IS-IS uses a two-level structure in an IS-IS domain. IS-IS devices are classified into the following levels:

Level-1 device: A Level-1 device manages intra-area routing. It establishes neighbor relationships with only Level-1 and Level-1-2 devices in the same area. Level-1 devices can be connected to other areas through Level-1-2 devices only.
Level-2 device: A Level-2 device manages intra-area routing. It establishes neighbor relationships with Level-2 devices in the same area and Level-1-2 devices in other areas only. All Level-2 devices form the backbone network of the routing domain. They are responsible for communications between areas. The Level-2 devices in the routing domain must be reachable, and no device of other levels is deployed between every two Level-2 devices.
Level-1-2 device: A Level-1-2 device can establish Level-1 neighbor relationships with Level-1 devices and Level-1-2 devices in the same area. It can also establish Level-2 neighbor relationships with Level-2 devices and Level-1-2 devices in other areas.
In most cases, Level-1 devices are located within an area, Level-2 devices are located between areas, and Level-1-2 devices are located between Level-1 devices and Level-2 devices.
The level of an IS-IS device and of an interface determine the level of a neighbor relationship. By default, neighbor relationships between two Level-1-2 devices are Level-1 and Level-2. To establish a Level-1 or Level-2 neighbor relationship, run the isis circuit-level command to modify the level of interfaces.
If only one area exists, setting the level of devices to Level-1 or Level-2 is recommended to prevent devices from maintaining two LSDBs that are the same. On an IP network, setting the level of all devices to Level-2 for future extension is recommended.
The is-level command is applicable to all topologies of the IS-IS process.

Prerequisites

An IS-IS process has been created using the isis command in the system view.

Configuration Impact

If the levels of IS-IS devices are changed during network operation, the IS-IS process will be restarted and IS-IS neighbor relationships will be disconnected. Setting the levels of Routers when configuring IS-IS is recommended.

Precautions

If neither Level-1 nor Level-2 is specified, the device works at Level-1-2. That is, the device calculates Level-1 and Level-2 routes and maintains Level-1 and Level-2 LSDBs.

Example

# Set the level of the device to Level-1.

<HUAWEI> system-view
[~HUAWEI] isis 1
[*HUAWEI-isis-1] is-level level-1