Campus Mobility
Core concepts
Campus mobility covers wireless architecture and roaming: controller-based vs. controller-less (ArubaOS 8 Gateway/MM vs. AOS-CX + Central), AP and client roaming (L2 vs. L3), mobility domains, and fast roaming (802.11r, OKC). Know the roles of the Mobility Master/Gateway, the difference between tunneled and bridged traffic, and how client VLAN assignment works across controllers. Understand band steering, airtime fairness, and RF arm/ARM (Adaptive Radio Management).
Traps to watch
- L2 vs. L3 roaming: L2 roaming keeps the client subnet; L3 roaming requires tunneling or mobility to preserve the IP. Questions test which mechanism preserves the session.
- 802.11r vs. OKC: Fast BSS transition (802.11r) vs. opportunistic key caching - know which is standards-based and which is vendor-assisted.
- Tunneled vs. bridged: Tunneled traffic goes to the controller/gateway; bridged stays local. Misconfiguring this breaks client VLAN assignment.
- ARM vs. manual RF: ARM automates channel/power; questions test when manual override is warranted (dense/high-interference areas).
Worked example
A client roams between APs on different subnets and loses its session. The fix is L3 mobility: configure the mobility domain so the client's anchor/tunnel preserves its original IP. If the client roamed within the same subnet, L2 roaming would suffice. The exam asks which mechanism is needed - answer: L3 mobility/tunneling across the mobility domain.
Rule of thumb
Match the roaming mechanism to the subnet topology: same subnet → L2 roaming; different subnet → L3 mobility with tunneling.