IS-IS

This help contains the following topics:

·     Introduction

¡     Network entities

¡     IS-IS areas

·     Configure IS-IS

¡     Configure an IS-IS instance

¡     Configure an IS-IS interface

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.

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

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

5.     Click Apply.