Network verification is a rapidly emerging technology that is a key part of Intent-Based Networking (IBN). Verification can help avoid outages, facilitate compliance processes and accelerate change windows. Full-feature verification solutions require an underlying mathematical model of network behaviour to analyze and reason about policy objectives and network designs. A mathematical model, as opposed to monitoring or testing live traffic, can perform exhaustive and definitive analysis of network implementations and behaviour, including proving network isolation or security rules. In this paper, we will describe how verification can be used in key IT processes and workflows, why a mathematical model is required and how it works, as well as example use cases from the Forward Enterprise platform. This will also clarify what requirements a mathematical model must meet and how to evaluate alternative products.