Connectivity
Core concepts
Connectivity covers how endpoints reach the network: PoE budgeting, LLDP/CDP neighbor discovery, uplink design, wireless client onboarding, and roaming infrastructure. Know PoE classes and the difference between PoE, PoE+, and PoE++ (802.3af/at/bt), plus how a switch budgets power across ports. Understand LLDP-MED for voice, and how AP uplinks (trunk vs. access, tagged management) are provisioned.
Traps to watch
- PoE budget oversubscription: A switch may advertise many PoE ports but only power a subset. Questions test whether you check the total wattage budget, not just port count.
- LLDP vs. CDP: Aruba uses LLDP; CDP is Cisco-proprietary but often enabled for compatibility. Know which is required for what (e.g., LLDP-MED for voice VLAN).
- AP uplink tagging: If the AP management VLAN is untagged on the switch port but the AP expects tagged, the AP never comes up.
- Speed/duplex mismatch causing late collisions and CRC errors - a recurring connectivity distractor.
Worked example
A switch has a 370 W PoE budget. Ten APs draw 25 W each (250 W) and five phones draw 12 W each (60 W) - total 310 W, within budget. Add one more 25 W AP and you hit 335 W; still fine. But if APs negotiate 802.3bt at 60 W each, ten APs alone exceed the budget. The exam tests whether you multiply class wattage by device count against the total budget.
Rule of thumb
Always compute total PoE draw against the switch's usable budget, and remember that negotiated class power - not nameplate - determines draw.