Advanced VLAN, Link Aggregation, and Spanning Tree Configuration
This domain tests how L2 topology is built and protected. Candidates must know port link-type semantics (access, trunk, hybrid) and how PVID and permitted-VLAN lists interact on trunk and hybrid ports. GVRP and VLAN mapping appear in questions about propagating or translating tags across domains. For aggregation, distinguish static vs dynamic (LACP) link aggregation, understand link-aggregation mode dynamic, and remember that member ports must match in speed, duplex, and VLAN configuration.
Spanning tree is the highest-yield area. Know STP, RSTP, PVST, and MSTP; MSTP uses regions defined by name, revision level, and VLAN-to-instance mapping - a mismatch in any of these puts a switch in a different region and breaks the intended topology. Traps include: which port becomes root/designated/alternate given cost and priority; the effect of stp edged-port (BPDU guard behavior); and root guard vs. loop guard placement. Another classic trap is assuming a blocked port forwards immediately after a topology change - RSTP uses proposal/agreement, so convergence is fast but still state-dependent.
Worked example: two core switches and four access switches. Give both cores identical MSTP region config and lower bridge priority (e.g., 4096 on primary, 8192 on secondary). Verify with display stp brief and display stp region-configuration. If an access switch unexpectedly becomes root, a lower-priority core likely has a region mismatch or a missing instance mapping.
Rule of thumb: always confirm region name, revision, and mapping match across all switches before troubleshooting individual port roles.