WAN

Wide Area Network

Pronunciation: WAN

Updated September 30, 20263 min read

In short

A WAN is a network that connects devices and local networks across large distances, such as cities or countries, often over links rented from telecom providers.

What is a WAN?

A WAN, or wide area network, is a network that spans a large geographic area and connects many smaller networks, such as the LANs of a company's offices in different cities. Where a LAN covers one building, a WAN can cover a region, a country, or the whole planet. The internet is the largest WAN in existence.

Organizations rarely own the cables a WAN runs over. Instead they lease connections from telecom providers, such as dedicated fiber lines or MPLS circuits, or they build encrypted VPN tunnels across the public internet, with routers at each site forwarding traffic over these links. SD-WAN (software-defined WAN) is a common modern approach in which software at each site chooses among several connections, such as fiber, broadband, and mobile data, based on cost and current performance. On a home router, the port labeled WAN is the one that connects to your internet provider, while the LAN ports connect your own devices.

If a LAN is the hallways inside one office building, a WAN is the highway system that connects that building to the company's other offices. WANs let branch offices reach shared data centers, let stores send sales data to headquarters, and connect cloud regions to each other. Because distances are long and links are shared or rented, WAN traffic is slower and more expensive than LAN traffic, so applications try to reduce round trips and cache data close to users.

A WAN is most often contrasted with a LAN. A LAN is local, fast, cheap per bit, and owned by one organization, while a WAN is wide, slower, higher in latency, and usually built on someone else's infrastructure. Between the two sits the MAN, a metropolitan area network that spans a single city. And the WAN IP address shown in a router's settings is simply its public address on the internet side.

Key takeaways

A WAN connects networks across long distances, such as offices in different cities or countries.
The internet is the largest WAN.
WAN links are usually leased from telecom providers or built as VPN tunnels over the internet.
WAN traffic has lower bandwidth, higher latency, and higher cost than LAN traffic.
A router's WAN port faces the internet provider, and its LAN ports face local devices.

Example

Why WAN links have higher latency: the speed of lightjavascript

// Light in optical fiber covers roughly 200 km per millisecond
const KM_PER_MS = 200;

function minRoundTripMs(distanceKm) {
  return (2 * distanceKm) / KM_PER_MS; // there and back, before any router delays
}

console.log(minRoundTripMs(0.1)); // 0.001 ms: two devices on the same LAN
console.log(minRoundTripMs(560)); // 5.6 ms: offices about 560 km apart
console.log(minRoundTripMs(5600)); // 56 ms: across an ocean, at best

Readers ask

What is the difference between a WAN and a LAN?

A LAN connects devices in one place, such as a home or office, and is fast and owned by one organization. A WAN connects networks across cities or countries, usually over leased lines or the internet, with lower bandwidth and higher latency.

Is the internet a WAN?

Yes. The internet is a global WAN made of thousands of independently run networks connected to each other. Company WANs often use the internet as one of their links, typically with VPN encryption on top.

What is the WAN port on a router?

The WAN port, sometimes labeled Internet, connects the router to your modem or internet provider. The router's other ports and its Wi-Fi form your LAN, and the router forwards traffic between the two sides.

Often compared

LAN vs WANA LAN connects devices in one building or site over fast, private links, while a WAN links networks across cities or countries, often over the internet.

WAN