📘 12-04: WAN Topologies & Modern WAN¶

🌍 WAN Topologies¶

Topology	Description	Trade-off
Point-to-point	One dedicated link between two sites	Simple; no redundancy
Hub-and-spoke	Remote sites (spokes) connect via a central hub	Cost-effective; hub is a SPOF, spoke-to-spoke is 2 hops
Full mesh	Every site links to every other site	Max redundancy/optimal paths; expensive
Partial mesh	Some direct links between key sites	Balance of cost and redundancy

📌 Redundancy at the Edge¶

Term	Meaning
Single-homed	One ISP, one link — no redundancy
Multihomed	Multiple ISPs/links (often via BGP) — failover + load sharing

🌍 SD-WAN¶

SD-WAN uses software-defined control to combine and intelligently steer traffic across multiple transports (MPLS, broadband, LTE) by application policy and link quality.

Reduces reliance on costly MPLS
Improves application performance and resilience
Central management across many sites

🌍 VPN as WAN¶

A site-to-site VPN over the public Internet provides WAN connectivity between offices at far lower cost than dedicated circuits — with an encrypted tunnel (usually IPsec), though performance depends on the Internet.

Tip

Key idea — WAN topologies trade cost vs. redundancy: hub-and-spoke (cheap, SPOF) → partial mesh → full mesh (redundant, costly). Multihoming adds ISP redundancy; SD-WAN and VPNs modernize and cut cost.

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