In the network shown in the figure, the R1 device is configured with route penetration. Then the R1 device sends the LSP of Level 1-2 to R3 so that R3 can learn the entire network route.

Question

Options

• ATRUE
• BFALSE

• A
  74% (17)
• B
  26% (6)

Explanation

Option A is correct because in IS-IS routing, a Level 1-2 router with route penetration (also called route leaking) configured is specifically designed to redistribute Level 2 (inter-area backbone) routing information downward into Level 1 LSPs. When R1 generates its L1 LSPs and floods them to neighboring L1 routers like R3, those LSPs carry the full network topology - including routes R3 would normally never see as a Level 1-only device. Without route penetration, R3 would only receive a default route pointing toward R1, giving it no visibility into the broader network.

Option B (FALSE) is wrong because route penetration is the exact mechanism that breaks the normal IS-IS boundary restriction - denying this contradicts how the feature works by design.

Memory tip: Think of route penetration as a "downward drip" - L2 routes drip down from the backbone into L1 areas via the L1-2 router. If the feature is enabled, the drip flows; if disabled, L1 routers are "sealed off" and only see a default route upward.

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