What are the modern alternatives to STP (Spanning Tree Protocol), and why are some networks moving away from it?

Some networks are transitioning to Layer 3 routing between switches, which handles redundancy without blocking ports.

Why move away from STP?

• STP (Spanning Tree Protocol) blocks redundant links — wasted bandwidth
• STP convergence (even RSTP (Rapid Spanning Tree Protocol)) isn't as fast or predictable as Layer 3 routing protocols
• Modern networks have grown from a few switches to hundreds or thousands with many VLANs (Virtual Local Area Networks)

The Layer 3 alternative:

• Use routed links between access, distribution, and core layer switches
• Layer 3 routing protocols (OSPF (Open Shortest Path First), EIGRP (Enhanced Interior Gateway Routing Protocol), BGP (Border Gateway Protocol)) handle redundancy without blocking ports
• All links can be active simultaneously (equal-cost multipath / ECMP (Equal-Cost Multi-Path))
• Only the connection from end devices to access layer switches remains Layer 2

STP still evolves:

• RSTP and MSTP (Multiple Spanning Tree Protocol) have improved convergence and scalability
• Many networks use a hybrid approach: Layer 3 in the core/distribution, Layer 2 + STP at the access layer

Tip: The trend in modern data center design (e.g., spine-leaf architecture) is to minimize Layer 2 domains and use Layer 3 everywhere possible.

Go deeper:

• TRILL (Wikipedia) — Perlman's own STP successor that uses all active links instead of blocking redundant ones.
• Shortest Path Bridging / 802.1aq (Wikipedia) — the IEEE replacement that keeps every path active with equal-cost multipath rather than pruning to one tree.