OSPF areas and backbone design — choose the correct statements Consider these statements about OSPF areas: You must configure separate loopback interfaces in each area. Area numbers can be assigned up to 65,535. The backbone area is called area 0. In a hierarchical design you do not need multiple areas. All areas must connect to area 0 (backbone), directly or via a virtual link. Which combination is correct?

Introduction / Context:
OSPF divides large networks into areas to improve scalability, reduce LSDB size, and speed convergence. Understanding the special role of the backbone (area 0) and how areas interconnect is essential for designing or troubleshooting multi-area deployments.

Given Data / Assumptions:

• We evaluate five statements regarding OSPF areas and backbone rules.
• We assume standard OSPF behavior without vendor-specific deviations.
• Virtual links may be used to logically connect an area to area 0 when no direct connection exists.

Concept / Approach:
The backbone is always area 0 and acts as the transit area for inter-area traffic. All other areas must connect to area 0, either directly or via a virtual link. Loopback interfaces are not required per area; they are commonly used for stable Router IDs. Area numbers are 32-bit; 65,535 is a valid decimal value but not the upper bound. Hierarchical designs typically use multiple areas; saying you do not need multiple areas contradicts the point of hierarchy.

Step-by-Step Solution:
Assess (1): False. Loopbacks are optional and not required per area.Assess (2): Misleading. Area IDs are 32-bit; limiting to 65,535 is not the absolute maximum.Assess (3): True. Area 0 is the backbone.Assess (4): False. Hierarchical OSPF motivates multiple areas.Assess (5): True. All areas must connect to area 0, possibly with a virtual link.Therefore, the correct combination is 3 and 5 only.

Verification / Alternative check:
Design guides consistently state area 0 as the backbone and require all other areas to be attached to it, directly or logically (virtual link), ensuring proper inter-area route distribution.

Why Other Options Are Wrong:

• B: Includes statement (2), which is not strictly correct as an upper bound claim.
• C/D/E: Include false statements (1 or 4) or omit requirement (5).

Common Pitfalls:
Assuming loopbacks are per-area requirements, or misreading the limits on area numbering. Also forgetting virtual links can satisfy the connection-to-backbone rule.

Final Answer:
3 and 5 only