A newly added VLAN for nurse-call system controllers sits on a switch several hops from the DHCP server, which lives on the core VLAN. None of the controllers receive an IP address, even though the VLAN and its interface are both configured and up. What is most likely missing?
Select an answer to reveal the explanation.
Short Explanation
DHCP requests start life as broadcasts, and broadcasts don't cross subnet boundaries on their own. Without something to scoop that broadcast up and forward it to the actual DHCP server, it just dies right there on the local VLAN. That scooping-up job belongs to a DHCP relay.
Full Explanation
A DHCP client's initial discovery message is a Layer 2 broadcast, and broadcasts are, by design, confined to their own subnet — a router or Layer 3 switch will not forward them onward by default, regardless of whether a route to the DHCP server's subnet exists. Because the VLAN and interface are already up, Layer 2 and basic Layer 3 addressing on the local segment are not in question; what's missing is the mechanism that converts that broadcast into a unicast request the remote DHCP server can actually receive, which is exactly what a DHCP relay (commonly configured as a helper or relay address pointing at the DHCP server) provides on the VLAN's Layer 3 interface. A missing static route would be a plausible cause if the symptom were unicast traffic failing to reach the server, but a route alone does nothing for a broadcast-based discovery message, and an ICMP-focused ACL or a trunk-tagging problem wouldn't explain devices failing to get an address specifically, since either would produce different, broader connectivity symptoms. The check is to look at the VLAN interface's configuration for a relay/helper entry pointing at the correct DHCP server address, and confirm it's present on every Layer 3 hop between the controllers and the server, not just the first one. A caveat: if multiple DHCP servers or scopes exist, the relay address must point at the right one, or requests will be forwarded successfully but simply never answered.