WAN
A wide-area network spanning sites and usually several providers.
Level: beginner
What is it?
A Wide Area Network links networks across large geographic areas, often using service-provider infrastructure, leased circuits, tunnels, or the public internet. Sites can communicate through routed IP connectivity without sharing the same local broadcast domain.
Why does it matter?
WANs connect branches, cloud networks, data centers, and remote users. Their design must handle latency, variable path quality, availability, provider boundaries, routing policy, and security across less-controlled infrastructure.
Mental model
Treat each site as an IP network attached to a wide-area path. Routers and overlay tunnels move packets between sites; local Ethernet details usually stop at the site edge.
How it works
- WAN links may be private, provider-managed, internet-based, or built using overlays such as VPN tunnels.
- Latency depends on distance, propagation, queueing, and routing path; bandwidth alone does not determine application responsiveness.
- Routing protocols and policy determine reachability between site prefixes.
- VPNs protect traffic across untrusted networks, but endpoints and routing configuration still need security controls.
- Redundancy can improve availability but needs correct failover and routing behavior.
Steps
- A branch host sends traffic toward a remote site prefix.
- The local gateway selects the WAN interface, provider path, or VPN tunnel.
- Intermediate routers forward the packet or tunnel encapsulation toward the remote gateway.
- The destination gateway routes the packet to its local subnet.
Real-world usage
- Connecting offices, cloud virtual networks, and remote workers.
- Comparing leased lines, internet VPNs, and managed SD-WAN approaches.
- Diagnosing high RTT, packet loss, and asymmetric routing.
Common mistakes
- Assuming a WAN means one specific technology.
- Confusing connectivity with encryption or authentication.
- Measuring only bandwidth while ignoring latency, jitter, and loss.
Interview questions
How does a WAN differ from a LAN?
A WAN connects geographically separated networks over broader routed/provider infrastructure; a LAN is local site infrastructure. Exact boundaries depend on administration and design.
Why may high-bandwidth WAN access still feel slow?
High round-trip latency, loss, queueing, and application request patterns can dominate even when raw bandwidth is high.