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Routing & Switching · Intermediate

IS-IS Level 1/2 Router

An IS-IS router participating in both levels, holding separate L1 and L2 databases, similar to an OSPF ABR.

Definition

L1/L2 routers inject L1 routes into L2 and set the Attached bit toward L1 routers to signal a path out of the area. Cisco IOS routers default to L1/L2, which can create unnecessary adjacencies and databases unless restricted.

Example

is-type level-1-2

Exam tip

Cisco defaults to level-1-2, so both L1 and L2 hellos are sent unless circuit-type is limited.

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