HW086: High Density Wi-Fi Part 2

The episode revisits a large high-density Wi-Fi deployment with listeners' follow-up questions. For DHCP management, the team implemented nine VLAN/gateway pools using RADIUS MAC authentication to randomly assign devices on first connection, with each MAC address remembering its VLAN assignment for a week. They discuss client isolation, explaining it prevents direct device-to-device communication but doesn't eliminate inter-client communication entirely—it just forces traffic through the router.

A significant discussion centers on bandwidth shaping and QoS. The speakers argue against bandwidth limiting on Wi-Fi, contending that capping individual user speed forces clients to consume more airtime by transmitting slower, which impacts all users in the area. They emphasize that in Wi-Fi environments, airtime is the constrained resource, not bandwidth. The team deployed three 10-gigabit WAN connections across nine gateways without implementing bandwidth shaping at either the Wi-Fi or WAN layer. They explain QoS requires end-to-end understanding from client through application to all network hops, and some applications don't respect QoS markings anyway. In this deployment, QoS was left at default settings, with audio-visual traffic isolated on a separate physical network entirely.

Regarding interference from non-owned access points, the team discovered numerous unauthorized APs (160MHz channels in 5GHz and misconfigured 2.4GHz radios) from vendors, contractors, and event staff. They used Wi-Fi Explorer Pro, CEDOS Wave, Wi-Fi Explorer Pi with Hamina Clip (which provides audio proximity feedback) to locate rogue devices. The approach emphasized cooperation over enforcement, noting that contractors legally have equal right to use unlicensed spectrum. They worked with device owners to either power down unnecessary APs or reconfigure problematic channels.

For band balancing and steering, the team deprecated forcible deauthentication-based band balancing in favor of BSS Transition Request signaling, which asks clients to move bands without forcing disconnection. With six-band capable clients comprising 60% of devices and 40% limited to 5GHz, they observed 6GHz clients spent approximately 90% of time on 6GHz APs (despite smaller cell sizes causing more frequent roaming than 5GHz clients).

The deployment used a single SSID covering both 5GHz and 6GHz, with band steering disabled and Reduced Neighbor Reporting (RNR) enabled. RNR allows 5GHz beacons to announce 6GHz AP availability with specific channel and SSID details, enabling direct client roaming without passive scanning. This simplified design contrasted with the previous year's separate 5/6GHz SSIDs, which caused confusion and roaming problems.

The speakers address device-type considerations, noting that while most devices were Apple (MacBooks, iPhones), Windows and Android devices present behaved similarly for RF principles, though they may roam differently based on chipset (Windows devices often less sticky, jumping between APs with smaller RSSI changes). The team tested roaming primarily with Apple devices.

On SSID quantity, the consensus recommends limiting to two SSIDs maximum (corporate and guest), with three as absolute maximum. They argue against separate 2.4/5/6 SSIDs, recommending instead one SSID for 2.4 only and one for 5/6 combined. Avoid duplicating the same SSID across multiple bands—let clients decide their band preference through steering mechanisms rather than manual selection.

Infrastructure considerations receive substantial attention. The deployment featured 10-gigabit connections to most access points (with few exceptions), UPS-backed switches in each data closet, and single-strand bidirectional single-mode fiber for backbone connectivity to the main distribution frame. Critical lesson: copper cabling runs near high-powered tri-phase cables caused interference and Wi-Fi service degradation. The team recommends Ethercon highly-shielded cabling for similar high-interference environments. Beyond cabling and power, network engineers must understand the entire ecosystem: what other systems share the switching fabric, whether audio-visual infrastructure uses the same network, and how all dependencies affect Wi-Fi reliability.