Which function is performed at the access layer of the three-layer hierarchical network design model?

Fault isolation is a distribution layer function, where route summarization and policy boundaries limit the blast radius of topology changes and link failures.

The access layer connects end-user devices and is the designated QoS trust boundary where traffic is classified and DSCP values are marked as traffic enters the network infrastructure. Marking at this layer ensures consistent QoS policy enforcement upstream through the distribution and core layers without relying on end-device markings.

Reliability through redundant hardware and high-availability designs is a core layer characteristic, ensuring uninterrupted high-speed transport between sites.

Fast transport of traffic at high speed with minimal processing is the primary role of the core layer, not the access layer.

Redundancy and load balancing between uplinks and VLANs are distribution layer responsibilities, providing resilient paths between access and core tiers.