Which methodology is the leading lifecycle approach to network design and implementation?

The Waterfall model is a generic sequential software development lifecycle and is not a network-specific design or implementation methodology.

PPDIOO - Prepare, Plan, Design, Implement, Operate, Optimize - is the Cisco lifecycle services approach that provides a structured, repeatable process covering every phase of network design and operation. It is the dominant framework referenced across Cisco certification tracks and enterprise design guidance, making it the recognized leading methodology for network lifecycle management.

The Spiral model is a risk-driven iterative software engineering framework and has no application as a network design lifecycle approach.

The V model maps software testing phases to development phases and is a software quality methodology, not a network design framework.