A Layer 3 link is used to connect two aggregation layer switches. Which kind of access layer topology design allows lot all access to aggregation uplinks to be active, but still have a backup in an…

A square looped topology activates all four links in the access-aggregation square simultaneously, meaning all uplinks are active and there is no standby backup path - contradicting the stated requirement.

A loop-free inverted topology typically has access switches connecting upward to only one aggregation switch, providing no redundant uplink and therefore no backup upon an uplink failure.

In a loop-free U topology, each access layer switch has dual uplinks - one to each aggregation switch - but Spanning Tree Protocol blocks one of those uplinks, leaving only a single active path per access switch. This satisfies the requirement that not all uplinks are simultaneously active while still providing a standby backup path that activates upon an uplink failure. The inter-aggregation link is a Layer 3 routed link, which breaks the Layer 2 loop and gives the topology its loop-free characteristic.

A triangle looped topology has all three links among the access and two aggregation switches active, which does not match the requirement for some uplinks to remain in a blocked standby state.