The company will triple in size over the next two years. How would you scale this network?
Show the answer
Say this first
Questions first: tripling where (same campus, new buildings, new cities, remote staff, acquisitions) and how applications change (more cloud, more data center, more video). Then I find what breaks first in today's design, usually the collapsed core's ports, layer 2 domains spanning closets, an address plan with no room to summarize, a single internet edge and manual operations. The answer is repeatable blocks: a dedicated core with standard distribution blocks or routed access, a summarizable address plan, scaled edges and automation from a source of truth, rolled out in phases.
Go deeper
What breaks first
| Area | Symptom |
|---|---|
| Collapsed core | Out of ports; one pair is the failure domain for the whole site |
| Layer 2 | VLANs spanning closets, big spanning trees, broadcast load |
| Addressing | No free blocks that summarize; overlaps with acquired companies |
| Internet edge | Circuit bandwidth, firewall sessions and throughput, one breakout for everyone |
| WAN | Hub tunnel capacity, per-site MPLS cost |
| Services | DHCP scopes, RADIUS and DNS capacity, licenses |
| Operations | Config drift, no inventory, a change backlog, the same two people doing everything |
Target design
- Campus: split out a core once there are several distribution blocks or buildings; routed access for new blocks.
- Addressing: a hierarchical plan by region and site with summaries at block and region edges, leaving room for acquisitions and cloud.
- Routing: one IGP with areas per building or region, BGP toward the WAN, cloud and internet.
- Edges: larger and diverse circuits, regional internet breakout, SD-WAN for branches, dedicated cloud connections (Direct Connect, ExpressRoute) once cloud traffic is steady.
- Operations: the team will not triple, so automation is the multiplier: a source of truth such as NetBox, templates, generated configs, compliance checks and CI for changes, monitoring that scales.
Phasing
- Foundations that do not touch users: IPAM and source of truth, monitoring, the new address plan, standards and templates.
- Build the new core in parallel and move one distribution block at a time.
- Scale the internet edge and WAN, then retire what is left of the old design.
Each phase has its own rollback and measurable exit criteria.
Tradeoff to name
Building ahead of growth costs capital early; building just in time risks outages during the growth itself. I would build the structure (core, addressing, automation) early and add capacity as it is needed.
They will ask next
What do you automate first?
The inventory and IP plan as a source of truth, then configuration backups and compliance checks, then templated builds for new access switches and branches. Those give quick wins and make every later change safer.
Traps
- Answering only with bigger boxes. Growth breaks structure and operations before it breaks bandwidth.