Which of the following are similarities between OSPF and IS-IS?

Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (OSPF vs. IS-IS Comparison):

C (Correct):

“Both OSPF and IS-IS support hierarchical design through the use of areas (OSPF Area 0 backbone; IS-IS Level 1/Level 2 hierarchy).”

D (Correct):

“Both protocols support variable length subnet masks (VLSM) and Classless Inter-Domain Routing (CIDR).”

Incorrect options:

A: Both use cost-based metrics, not hop count.

B: Both protocols converge quickly (they are link-state protocols).

E: IS-IS uses Layer 2 (CLNS) for communication, not Layer 3 multicast.

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These answers are fully in line with Nokia’s official service router certification curriculum.