Match each IS-IS term to its definition.
Drag a concept onto its matching description — or click a concept then click the description.
Link State PDU containing routing information
Designated Intermediate System on a broadcast network
Network Service Access Point, the IS-IS address
Subnetwork Point of Attachment, e.g., MAC address
IS-IS Hello PDU used for neighbor discovery
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
IS-IS Area: A set of routers sharing the same area address.
In IS-IS, an area is identified by a common area address, LSPs carry link state data, and Level-1 routers operate intra-area. Common confusions involve swapping area definitions (system ID vs. area address) and mixing Level-1/Level-2 roles.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
IS-IS Area: A set of routers sharing the same area address.
Why this is correct
IS-IS areas are defined by a common area address in the NET; routers in the same area share that address.
LSP (Link State PDU): A packet containing link state information.
Why this is correct
LSPs are the fundamental data units in IS-IS that carry topology and link state information between routers.
Level-1 Router: Routes within an area.
Why this is correct
Level-1 routers operate within a single IS-IS area and maintain the area's topology.
IS-IS Area: A set of routers sharing the same system ID.
Why it's wrong here
Incorrect — the system ID uniquely identifies a router; an area is defined by a common area address, not system ID.
Level-1 Router: Routes between areas.
Why it's wrong here
Incorrect — routing between areas is performed by Level-2 routers; Level-1 routers only route within their area.
Visual reference
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Senior Network & Security Engineer · founder of Courseiva
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