A WAN connects geographically separated networks via service providers using dedicated, packet-switched or internet-based technologies.
WAN topologies
| Topology | Description | Pros | Cons |
|---|---|---|---|
| Point-to-point | Direct link between 2 sites | Simple, low latency | Expensive, poor scaling |
| Hub-and-spoke | Central hub, several spokes | Cheap, easy to manage | Single point of failure |
| Full mesh | All sites connected | High redundancy | Very expensive |
| Partial mesh | Some direct links | Balanced | More complex routing |
Traditional WAN technologies
- Leased lines: dedicated physical link (T1/E1, fiber), fixed bandwidth, low latency. Encapsulation: HDLC (Cisco proprietary), PPP (standard, authentication + multilink):
interface Serial0/0/0
encapsulation ppp
ip address 10.0.0.1 255.255.255.252- Circuit-switched: PSTN, ISDN (legacy – theory only)
- Packet-switched legacy: Frame Relay, ATM (know the concepts, not the config)
- MPLS: label-based forwarding, QoS-aware, VPN separation – see the MPLS post
- Ethernet WAN: provider-delivered Ethernet – “long LAN”: Metro Ethernet, E-Line (P2P), E-LAN (multipoint)
Internet-based WAN
| Technology | Media |
|---|---|
| DSL | Copper |
| Cable | Coax |
| Fiber | Fiber |
| LTE / 5G | Wireless |
| Satellite | Wireless |
Often combined with NAT, VPN and SD-WAN.
SD-WAN (very CCNP relevant)
Problem: MPLS is expensive, routing is static, cloud performance is poor. Solution: a central controller, application-based routing over multiple transports (MPLS + internet). Features: path selection by latency/jitter/packet loss, zero-touch provisioning, central policy control. SD-WAN = control plane separated from data plane.
Comparison
| Technology | Cost | Performance | QoS | Scalability |
|---|---|---|---|---|
| Leased line | High | High | Yes | Low |
| MPLS | High | High | Yes | High |
| Ethernet WAN | Medium | High | Yes | Medium |
| Internet VPN | Low | Varies | Limited | High |
| SD-WAN | Medium | Optimized | Advanced | Very high |
WAN QoS
Voice/video are latency-sensitive, and WAN links are often the bottleneck – MPLS and SD-WAN support end-to-end QoS.
Exam tips 🔥
- Know MPLS vs internet VPN
- Understand hub-and-spoke vs mesh
- On WAN, latency, jitter and loss matter more than bandwidth