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Routing & Switching · Intermediate

IS-IS Level 2

Inter-area (backbone) IS-IS routing between L2 and L1/L2 routers, which may be in different areas.

Definition

The Level 2 backbone must be contiguous and carries routes between areas. L2 adjacencies can form between routers with different area addresses. Many SP networks run a single flat L2 domain for simplicity.

Example

is-type level-2-only

Exam tip

The IS-IS backbone is a chain of L2-capable routers, not a numbered area like OSPF area 0.

Related terms