Devices in a new VLAN get no IP address
Layer-2 broadcast does not cross a router. Without DHCP relay (ip helper), clients in a different VLAN than the DHCP server stay silent.
Try this first
- 1Confirm the VLAN is otherwise healthy. Set a static IP on a laptop and try to ping the gateway. Works? Routing is fine.
- 2On the gateway or L3 switch: configure ip helper-address (Cisco) or dhcp-relay (Aruba/Mikrotik) pointing at the DHCP server.
- 3Make sure the DHCP server actually has a scope for the new subnet. Without a scope, relay requests get no reply.
- 4Test with a fresh client. A packet capture on the DHCP server shows whether relay requests truly arrive, that is the fastest check.
When to bring us in
With multiple DHCP servers, redundant gateways, or a Windows DHCP failover pair, the config gets fussy. We do this daily, bring us in for the design.
See also
- Wi-Fi drops randomly across the officeFirst rule out whether it is the access points or the internet connection itself. Different fix.
- One room or corner has no or bad Wi-FiNot always "add another AP"; often one is poorly positioned, or there is a metal wall in the way.
- Internet is suddenly slow for everyoneThree suspects: your provider, a colleague soaking the line, or a backup or update kicking in unexpectedly.
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