Network Design and Architecture
Core design concepts
Aruba designs are organized around the mobility controller (or controller-less Instant/Gateway) as the policy and forwarding anchor, with APs terminating tunnels via GRE or using bridge/local forwarding. A candidate should be fluent in the vocabulary of campus core–aggregation–access hierarchy, overlay vs. underlay, mobility master/local topologies, and the difference between tunnel mode, bridge mode, and mixed mode forwarding. Understand capacity planning: client count per controller, tunnel throughput, and MTU implications of GRE encapsulation.
Traps to expect
Questions often conflate control plane reachability with data plane forwarding. A design can have APs registered to a controller while user traffic is locally bridged. Another common trap is assuming a single large controller replaces redundancy - design questions reward N+1 or active-standby thinking, not raw port counts. Watch for MTU math: GRE adds overhead, so underlay MTU must accommodate encapsulated frames or fragmentation/PMTUD issues appear.
Rule of thumb
Size controllers for peak concurrent clients at ~80% licensed capacity and verify tunnel throughput against uplink bandwidth, not just AP counts. For a 500-AP campus with 20 clients/AP peak, plan ~10,000 client licenses across a redundant pair rather than one 12,000-license chassis.
Design vocabulary to know
Redundancy models (N+1, active-active, active-standby), mobility domains, and the role of the mobility master in multi-controller hierarchies.