LLD vs HLD for network engineers.
Two documents, two audiences, two levels of detail. The High-Level Design is the blueprint an architect gets signed off; the Low-Level Design is the build sheet an engineer configures from. This page sets out exactly what belongs in each, and where the boundary sits.
LLD — Low-Level Design
In networking, LLD stands for Low-Level Design. It is a detailed technical plan that provides specific instructions and configurations for implementing a network based on the High-Level Design (HLD) or architectural plan. The Low-Level Design bridges the gap between the high-level conceptual view of the network and the actual implementation details.
The Low-Level Design delves into the specifics of each network component, such as routers, switches, firewalls, and other devices, as well as the configurations and protocols needed to realize the desired network architecture and functionality. It includes detailed information on IP addressing, routing protocols, security policies, Quality of Service (QoS) settings, VLAN configurations, and more.
Key components of a Low-Level Design
The Low-Level Design provides network administrators and engineers with a step-by-step guide to configure and deploy the network according to the high-level requirements and objectives defined in the High-Level Design. It ensures consistency, accuracy, and proper implementation of the network, leading to a reliable, efficient, and secure network infrastructure.
HLD — High-Level Design
In networking, HLD stands for High-Level Design. It is a strategic and abstract representation of the overall network architecture and design that outlines the key components, major connectivity requirements, and high-level interactions between different elements of the network. The High-Level Design serves as a blueprint or roadmap for building the network, providing a broad overview of the network's structure and functionality.
Key elements of a High-Level Design
The High-Level Design is not as detailed as the Low-Level Design (LLD), which provides specific configurations and implementation instructions. Instead, the HLD focuses on the big picture, capturing the network's requirements, objectives, and major components without getting into the technical specifics.
LLD vs HLD compared
| Aspect | Low-Level Design (LLD) | High-Level Design (HLD) |
|---|---|---|
| Focus | Detailed technical plan and configurations | Strategic and abstract overview |
| Level of Detail | Specific implementation instructions | Broad architectural representation |
| Components | Device configurations, IP addressing, routing protocols, etc. | Network topology, layers, connectivity requirements, etc. |
| Scope | Specific to each network component | Overall network structure and functionality |
| Configurations | Precise configurations and settings for each device | High-level decisions on technology and protocols to be used |
| Interactions | Detailed interactions between devices | High-level interactions between major components |
| Purpose | Guides network implementation and deployment | Serves as a blueprint or roadmap for network architects |
| Audience | Network engineers and administrators | Stakeholders, project managers, and network architects |
| Timeframe and Budget | Taken into account during implementation | Rough estimate for project planning and resource allocation |
| Level of Abstraction | Low-level view of specific details | High-level view of network architecture |
| Deliverables | Detailed documentation and configurations | High-level network design documents |
| Connection to HLD | Derives from and elaborates on the HLD | Lays the foundation for the LLD |
Which comes first, and why the order matters
Once the High-Level Design is completed and approved, it serves as a foundation for the Low-Level Design, where engineers and administrators create detailed configurations and implement specific network technologies to realize the network's objectives as outlined in the HLD.
In summary, the Low-Level Design provides specific instructions and configurations for the implementation of each network component, while the High-Level Design focuses on the overall network architecture and its major components without diving into specific configurations. The HLD serves as a blueprint for the LLD, allowing network architects to plan the network structure and functionality before moving into detailed technical planning during the LLD phase.
Frequently asked
What is the difference between HLD and LLD in networking?
The High-Level Design describes what the network is and why — topology, layers, connectivity requirements, security architecture, scalability. The Low-Level Design describes exactly how to build it — device-by-device configurations, IP addressing schemes, routing protocol settings, VLANs, ACLs and QoS policies. HLD is written for stakeholders, project managers and network architects; LLD is written for the engineers who will type the commands. The HLD is approved first and becomes the foundation the LLD elaborates on.
Which comes first, HLD or LLD?
HLD comes first. Once the High-Level Design is completed and approved, it serves as a foundation for the Low-Level Design, where engineers and administrators create detailed configurations and implement specific network technologies to realize the network's objectives as outlined in the HLD. Attempting an LLD before the HLD is signed off usually means reworking configurations when the architecture changes.
What does an LLD network diagram show that an HLD diagram does not?
An HLD diagram shows the shape of the network: sites, core/distribution/access layers, WAN links, internet edge and where firewalls sit. An LLD diagram adds the detail you cannot deploy without — interface numbers, IP addresses and subnet masks, VLAN IDs, routing protocol areas and process IDs, HSRP/VRRP groups and physical port assignments. If a diagram tells you which port a cable goes into, it is an LLD diagram.
Who writes the HLD and who writes the LLD?
The HLD is typically produced by network architects and pre-sales or solution-design teams, because its audience is stakeholders, project managers and network architects who need to approve scope, budget and timeline. The LLD is produced by network engineers and administrators — the people who will implement and later troubleshoot the network. In smaller organisations the same person often writes both, but the two documents still serve different readers.
Are HLD and LLD used outside networking?
Yes. The same two-tier split is standard in software engineering and in telecom projects, where HLD and LLD mean much the same thing — an architectural document followed by an implementation-detail document. The vocabulary in this article is networking-specific (VLANs, routing protocols, QoS), but the underlying distinction between an approved blueprint and the detailed build instructions is the same discipline.
Network design is one of the topics covered in the free fundamentals library — including network design and architecture, network topologies and OSPF.
Reviewed by Vikas Swami · Founder, Networkers Home · Dual CCIE #22239 · Last updated 2026-08-29