is-level

Function

The is-level command sets the level of an IS-IS switch.

The undo is-level command restores the default setting.

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

Format

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

undo is-level

Parameters

Parameter	Description	Value
level-1	Indicates that the level of the switch is Level-1. The switch calculates only intra-area routes and maintains the Level-1 LSDB.	-
level-1-2	Indicates that the level of the switch is Level-1-2. The switch calculates Level-1 and Level-2 routes and maintains Level-1 and Level-2 LSDBs.	-
level-2	Indicates that the level of the switch is Level-2. The switch calculates only Level-2 routes, and maintains the Level-2 LSDB.	-

Views

IS-IS view

Default Level

2: Configuration level

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 routing domain. IS-IS switches are classified into the following levels:

Level-1 switch: A Level-1 switch manages intra-area routing. It establishes neighbor relationships with only Level-1 and Level-1-2 switches in the same area. Level-1 switches can be connected to other areas through Level-1-2 switches only.
Level-2 switch: A Level-2 switch manages intra-area routing. It establishes neighbor relationships with Level-2 switches in the same area and Level-1-2 switches in other areas only. All Level-2 switches form the backbone network of the routing domain. They are responsible for communications between areas. The Level-2 switches in the routing domain must be reachable, and no switch of other levels is deployed between every two Level-2 switches.
Level-1-2 switch: A Level-1-2 switch can establish Level-1 neighbor relationships with Level-1 switches and Level-1-2 switches in the same area. It can also establish Level-2 neighbor relationships with Level-2 switches and Level-1-2 switches in other areas.

In most cases, Level-1 switches are located within an area, Level-2 switches are located between areas, and Level-1-2 switches are located between Level-1 switches and Level-2 switches.

The level of an IS-IS switch and of an interface determine the level of a neighbor relationship. By default, neighbor relationships between two Level-1-2 switches 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 switches 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 switches to Level-2 for future extension is recommended.

Precautions

If the levels of IS-IS switches are changed during network operation, the IS-IS process will be restarted and IS-IS neighbor relationships will be disconnected. Setting the levels of switches when configuring IS-IS is recommended.
If the Level-1 and Level-2 is not specified, the switch works at Level-1-2. That is, the switch calculates Level-1 and Level-2 routes and maintains Level-1 and Level-2 LSDBs simultaneously.
When both Level-1 and Level-2 switches have routes destined for the same destination address, the route on the Level-1 switch is preferred.

Example

# Set the level of the current switch to Level-1.

<HUAWEI> system-view

[HUAWEI] isis 1

[HUAWEI-isis-1] is-level level-1