IS-IS

Introduction

IS-IS is a link-state interior gateway protocol (IGP) used within an AS. It uses the SPF algorithm for route calculation.

Network entities

A network entity title (NET) identifies the network layer information of an IS. It does not include transport layer information. A NET is a special NSAP address with the SEL being 0. The length of a NET is in the range of 8 to 20 bytes, same as a NSAP address.

A NET includes the following parts:

• Area ID—The length of an area ID is 1 to 13 bytes.

• System ID—A system ID uniquely identifies a host or router in the area and it length is fixed at 6 bytes.

• SEL—The SEL value is 0 and the length is fixed at one byte.

For example, for a NET ab.cdef.1234.5678.9abc.00, the area ID is ab.cdef, the system ID is 1234.5678.9abc, and the SEL is 00.

Typically, a router only needs one NET, but it can have a maximum of three NETs for smooth area merging and partitioning. When you configure multiple NETs, make sure they have the same system ID.

IS-IS areas

IS-IS has a 2-level hierarchy to support large-scale networks. A large-scale routing domain is divided into multiple areas. Typically, a Level-1 router is deployed within an area. A Level-2 router is deployed between areas. A Level-1-2 router is deployed between Level-1 and Level-2 routers.

• Level-1 router

  A Level-1 router establishes neighbor relationships with Level-1 and Level-1-2 routers in the same area. It maintains an LSDB comprising intra-area routing information. A Level-1 router forwards packets destined for external areas to the nearest Level-1-2 router.

  Level-1 routers in different areas cannot establish neighbor relationships.

• Level-2 router

  A Level-2 router establishes neighbor relationships with Level-2 and Level-1-2 routers in the same area or in different areas. It maintains a Level-2 LSDB containing inter-area routing information. All the Level-2 and Level-1-2 routers must be contiguous to form the backbone of the IS-IS routing domain.

  Level-2 routers can establish neighbor relationships even if they are in different areas.

• Level-1-2 router

  A router with both Level-1 and Level-2 router functions is a Level-1-2 router. It can establish Level-1 neighbor relationships with Level-1 and Level-1-2 routers in the same area. It can establish Level-2 neighbor relationships with Level-2 and Level-1-2 routers in different areas. A Level-1 router can reach other areas only through a Level-1-2 router. The Level-1-2 router maintains two LSDBs, a Level-1 LSDB for intra-area routing and a Level-2 LSDB for inter-area routing.

vSystem support information

Support of non-default vSystems for this feature depends on the device model. This feature is available on the Web interface only if it is supported.

Configure IS-IS

Configure an IS-IS instance

1. Click the Network tab.

2. In the navigation pane, select Routing > IS-IS.

3. Click Create.

4. Configure the IS-IS instance parameters.

   Table-1 IS-IS instance parameters

   Item	Description
   Instance ID	Specify an instance ID.
   Level	Specify an IS level. Options include Level-1, Level-2, and Level-1-2: Level-1—A Level-1 router maintains a Level-1 LSDB comprising intra-area routing information. Level-2—A Level-2 router maintains a Level-2 LSDB containing inter-area routing information. Level-1-2—A Level-1-2 router has both Level-1 and Level-2 router functions. It maintains two LSDBs, a Level-1 LSDB for intra-area routing and a Level-2 LSDB for inter-area routing.
   Network entity title	Specify a network entity title for the IS-IS process. A network entity title is a dotted hexadecimal string in X…X.XXXX....XXXX.00 format. The X…X segment represents the area address, the XXXX....XXXX segment represents the system ID, and the 00 segment is the SEL.

5. Click OK.

   The IS-IS instance will be displayed on the IS-IS instance page.

Configure an IS-IS interface

1. Click the Network tab.

2. In the navigation pane, select Routing > IS-IS.

3. Click the Interface List tab.

4. Configure the following interface parameters as needed.

   Table-2 IS-IS interface parameters

   Item	Description
   Interface	Interface that runs IS-IS.
   IS-IS enabling state	Select whether to enable IS-IS on the interface and specify a circuit level. Level options include Level-1, Level-2, and Level-1-2. For an interface of a Level-1 router, the circuit level can only be Level-1. For an interface of a Level-2 router, the circuit level can only be Level-2. For an interface of a Level-1-2 router, you must specify a circuit level to form only the specified level neighbor relationship.
   Level-1 link cost	Specify the link cost used for Level-1 route calculation.
   Level-2 link cost	Specify the link cost used for Level-2 route calculation.

5. Click Apply.