is-level

Function

The is-level command configures the level of IS-IS devices.

The undo is-level command restores the default setting.

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	Indicates a router at Level-1. It calculates only the intra-area routes and maintains the LSDBs of Level-1.	-
level-1-2	Indicates a route at Level-1-2. It calculates both the Level-1 and Level-2 routes and maintains the LSDBs of Level-1 and Level-2.	-
level-2	Indicates a route at Level-2. It calculates the Level-2 routes and maintains the LSDBs of Level-2.	-

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 domain. IS-IS devices are classified into the following levels:

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

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

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 routers 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 routes to Level-1 or Level-2 is recommended to prevent routes from maintaining two LSDBs that are the same. On an IP network, setting the level of all routes to Level-2 for future extension is recommended.

Prerequisites

An IS-IS process has been enabled 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 routes when configuring IS-IS is recommended.

Precautions

If the Level-1 and Level-2 is not specified, the route works at Level-1-2. That is, the route calculates Level-1 and Level-2 routes and maintains Level-1 and Level-2 LSDBs simultaneously.

Example

# Set the current route at Level-1.

<sysname> system-view

[sysname] isis 1

[sysname-isis-1] is-level level-1