Data Center HLD vs LLD: What Should Each Document Contain?

HLD and LLD serve different purposes.

HLD

The High Level Design communicates the architecture, major components, topology, technology choices, security zones, connectivity and design principles.

LLD

The Low Level Design translates the approved architecture into implementation details such as interfaces, IP addresses, VLANs, VRFs, routing parameters, device naming, port mapping and validation requirements.