In a routed access hierarchical campus design, the access-to-distribution Layer 2 uplink trunks are replaced with Layer 3 point-to-point routed links. Why is it recommended that VLANs are confined on

Convergence time is improved by replacing L2 trunks with L3 links because routing protocols converge faster than STP, but this is a property of routed access in general and is not specifically dependent on whether VLANs span multiple access switches.

Layer 2 loops are prevented by the routed access design itself because L3 point-to-point links break the L2 domain; VLAN scoping to a single switch does not add further loop prevention.

Fault isolation is a benefit of routed access design broadly, but the specific failure scenario that VLAN confinement addresses is the routing black hole, not general fault isolation.

In a routed access model, each access switch has a directly connected subnet per VLAN. If a VLAN spans two access switches and the uplink from one switch fails, the distribution layer router still has a route pointing toward that subnet via both switches, but traffic sent toward the switch with the severed path is silently dropped - a routing black hole. Confining each VLAN to a single access switch ensures the subnet is reachable through exactly one upstream routed link, eliminating this ambiguity.