What is DHCP?
Definition
DHCP, the Dynamic Host Configuration Protocol, automatically gives each device that joins a network its IP address, default gateway and DNS servers. A DHCP server keeps a pool of addresses, called the scope, and lends them to devices for a set period, called the lease time.
DHCP explained
Every device on a WiFi network needs an IP address before it can do anything, including load a captive portal. When a phone joins, it broadcasts a request, the DHCP server offers an address from the scope, and the device accepts it for the length of the lease. In larger networks, an IP helper or relay on the router forwards those requests to a central server.
DHCP is a common failure point in busy venues. Scope exhaustion happens when every address in the pool is in use and new devices cannot connect, which is the most frequent failure at events. MAC randomisation makes it worse, because a device that reconnects with a new address can take a second lease.
The fixes are planning rather than hardware. Size subnets for peak attendance, for example a /21 or /20 for a large event, and set short leases of 30 to 60 minutes on guest networks so addresses recycle as people come and go. Watch for rogue DHCP servers and misconfigured relays, which cause timeouts that look like WiFi problems but are not.
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