Failure of dhcp server failover

[Simon Hobson]

Eugene Grosbein <eugen at grosbein.net> wrote:

> I have several UniFi wireless access points (AP) controlled by UniFi Controller software.
> These access points act as transparent L2 bridges supporting several distinct WLANs and vlans
> for their wireless clients plus extra management vlan. They have wired uplink connected
> to L2 manageable switches that insert DHCP option 82 to all request from AP themselves and their clients.
> Mentioned vlans are routed by Cisco routers acting as DHCP relays. These routers relay DHCP requests
> to pair of ISC DHCP Servers. There is ordinary IP pool for wireless clients and it works just fine.
> 
> UniFi access points theyselves obtain their IP addressess and additional DHCP vendor options from DHCP servers.
> Each AP makes use of at least two IP addresses, one per vlan.

I'm using UniFi APs and they only get one address - on the management VLAN. They certainly do not get any other addresses - I've just checked the leases file at work to confirm.
This is the case both in the office (HP switch), and on a customer site (Cisco switches).

Could it be that your VLANs are not properly configured, and so your DHCP server is seeing one DHCP request from the AP repeated across multiple virtual interfaces ?
As pointed out before, if everything is correctly configured then the DHCP server will automagically work out the right subnet based on either the interface for non-relayed packets, or the GIAddr for relayed packets.