Topologies: point-to-point (simple, costly), hub-and-spoke (cheap, hub = SPOF), full/partial mesh. Legacy still in syllabus as concepts: circuit-switched (PSTN/ISDN) and packet-switched (Frame Relay, ATM) — know the idea, not the config.

• Leased line: dedicated, constant bandwidth, encapsulation HDLC (Cisco default) or PPP (standard, CHAP/PAP, multilink).
• Ethernet WAN: Metro-Ethernet — E-Line (P2P), E-LAN (multipoint); feels like a long LAN.
• MPLS VPN: provider-managed, QoS-aware, private separation — see the MPLS post.
• Internet VPN / SD-WAN: cheap underlay, software overlay steering per application/SLA.

Metrics that decide design: latency, jitter, packet loss, SLA. Modern default: dual internet + SD-WAN overlay, MPLS kept only where QoS guarantees still pay.