Auditorium Capacity and DHCP Failures After WLAN Refresh
A 220-AP office deployment serves 1,100 employees and up to 2,500 guests across five buildings. The auditorium has 30 APs, 1,200 seats, and hosts weekly all-hands meetings. WLANs are CORP (WPA2-Enterprise, 5 GHz preferred), GUEST (PSK portal), and IOT (PSK, 2.4 GHz only). After a 4K video rollout, users report stalls in the auditorium. Mist Wireless Assurance shows auditorium SLEs: Capacity 72%, Coverage 88%, Roaming 81%, DHCP 64%, AP Health 95%. During the last event, 980 clients associated, 5 GHz retry rate was 38%, 2.4 GHz retry rate was 62%, and 14% of CORP clients failed DHCP on VLAN 210. Roaming failures were 9%, mostly between auditorium APs. The network team proposes adding 10 APs and widening channels to 80 MHz.
1. Which SLE should be investigated first, and what evidence distinguishes a wireless capacity problem from a DHCP/VLAN problem?
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Investigate DHCP first because it is the lowest SLE and because DHCP failure is not automatically a Wi-Fi symptom. Pull the client timeline for several affected CORP clients and confirm whether the client associated successfully, reached the DHCP stage, and then timed out. Compare a wired client on VLAN 210 and check the DHCP scope utilization, relay configuration, and the switch trunk carrying VLAN 210. If the scope is exhausted, the relay is missing, or wired clients also fail, the root cause is the DHCP/VLAN path, not RF. Capacity is still a concern: 980 clients on 30 APs with 38% retry on 5 GHz and 62% on 2.4 GHz indicates airtime contention and likely co-channel interference. Widening to 80 MHz would make that worse by reducing the number of non-overlapping channels. Treat the two problems as separate: fix DHCP/VLAN first, then tune RF and capacity.
2. Recommend WLAN/RF changes for the auditorium and justify each.
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For a high-density auditorium, reduce channel width on 5 GHz to 40 MHz or 20/40 MHz rather than 80 MHz; wider channels increase co-channel interference in a dense AP grid. Enable band steering so capable clients move to 5 GHz, but keep IOT on its own 2.4 GHz WLAN. Disable low 2.4 GHz rates such as 1, 2, 5.5, and 11 Mbps to reduce management and multicast airtime. Enable 802.11k/v-assisted roaming so clients have neighbor reports and can transition between auditorium APs more cleanly. Consider lowering transmit power on densely packed APs to shrink cells and improve spatial reuse, then validate coverage at the edges. Do not add 10 APs blindly; first fix the channel plan and DHCP, then use the Capacity SLE and RF neighbor data to decide whether additional APs are needed and where.
3. How would you validate the changes and avoid repeating the failure at the next event?
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Capture a baseline before the next all-hands: auditorium Capacity, Coverage, Roaming, and DHCP SLEs, per-AP channel and power, retry rates, and DHCP scope utilization. After the changes, run a controlled test with 100 to 200 clients before the full event, then monitor the same metrics live. Use Mist client events to confirm that CORP clients complete DHCP on VLAN 210 and that roaming between auditorium APs improves. Check that the DHCP scope has headroom for the full 980-client peak and that the relay and trunk are healthy. After the event, compare before-and-after SLE trends and document the channel plan and power settings as the auditorium standard. This separates the DHCP fix from RF tuning and prevents a repeat of the same failure.