Which of the following statements are true about IS-IS? (Select two.)

Question

Options

• AIS-IS supports a larger number of routers per area than OSPF.
• BIdeally, both IS-IS and OSPF should not be designed with more than 300 routers per area.
• CIS-IS maintains separate LSDB and LSPs per level.
• DIS-IS floods the same LSPs to update both L1 and L2 LSDBs.
• EOptimal routing cannot be achieved when IS-IS is designed with multiple levels over a network

• A
  90% (38)
• B
  2% (1)
• C
  2% (1)
• E
  5% (2)

Explanation

A is correct: IS-IS operates at Layer 2 (directly over the data link layer), giving it a more efficient flooding mechanism than OSPF. This allows IS-IS to support significantly more routers per area than OSPF, which is constrained by IP-based flooding overhead. D is correct: In IS-IS, an L1/L2 router does not generate separate sets of LSPs for each level. Instead, it floods the same LSPs into both the L1 and L2 LSDBs on the local router. This differs from OSPF, where an ABR generates distinct LSAs for each area. B is false because OSPF's practical per-area limit is much lower (around 50 routers), not 300 like IS-IS. C is false because it directly contradicts D - IS-IS does NOT maintain separate LSPs per level; the same LSPs populate both databases. E is false because optimal routing can absolutely be achieved with a well-designed multi-level IS-IS hierarchy.

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