NetIntent

🎯 What it is:

NetIntent is a Python engine that builds a model of a Cisco network from its configurations and answers reachability questions against it: does a flow get through, and if not, where and why is it stopped. It verifies declared intents and, crucially, simulates a proposed change on a copy of the model so a change that would break connectivity is caught before it is ever pushed to a device. Built and demonstrated on a GNS3 lab.

❓ The problem:

Before pushing a configuration change to a live network, there is no easy way for a small team to know whether it will break something. An ACL edited a little too broadly, a link taken down for maintenance that turns out to be the only path, a static route that shadows another — each is a one-line change that can take a service offline, and each is usually only discovered after it is pushed.

⚙️ What it does:

• Parses each device's config into a model — interfaces and their subnets, ACLs (named and numbered, standard and extended, matched bit for bit against Cisco wildcard masks), static routes and a simplified OSPF

• Builds each device's routing table (connected, static and OSPF shortest path) and traces a packet hop by hop, applying every ACL inbound and outbound exactly where a router would

• Verifies intents — flows that must be reachable or blocked — and reports each with the path it takes

• Simulates a proposed change on a copy of the model and reports the impact: which intents it would break, and the exact ACL or missing route responsible

• Appends every verification and simulation to an audit log

🧰 Tech stack:

• Device access — Netmiko (SSH); console for the GNS3 lab

• Address maths — the standard-library ipaddress module (exact, no dependencies)

• Config parsing — a small, purpose-built IOS parser

• Model — connected / static / simplified-OSPF routing plus ACLs

• Lab build — GNS3 v2 REST API