We have a cabinet of dedicated servers with a Brocade FESX648-PREM switch at the top. We own all the hardware and all the MAC addresses are known to us. We also fully manage the servers so we retain administrative access, but our customers have administrative access as well.
Currently we use VLANs and subnets to isolate the servers, prevent IP hijacking, etc. However, we want to make more efficient use of our IPv4 allocations. We lose a lot of usable IPs for gateway purposes and we have an abundance of subnets too small for many customer needs.
I've considered progressively migrating the servers to a single VLAN and use static ARP to prevent IP hijacking. We'd lose layer 2 isolation, but I'm not sure what sort of abuse that would open us up to.
What are the dangers of placing all of our servers on a single VLAN with only static ARP bindings to prevent IP hijacking? In other words, what forms of abuse would be possible with a single VLAN config that would not be possible with every server on its own VLAN? Are there any precautions we can take to prevent the abuse while achieving our goals of more efficient IPv4 usage?