Running a network behind a ZyWall USG 200. Our subnet has around 100-110 devices connected at any particular time. Recently some users were having trouble with getting a DHCP address (keep getting self-assigned IPs) and upon investigation I noticed that there were 150-200 addresses assigned in the DHCP table on the router. I looked into the table and it is showing one or two devices with 30-50 IPs assigned:


I think that this is filling up the available address range and preventing other devices from leasing an IP. Interestingly, as I refresh the table this number fluctuates and different devices are hogging the addresses.

Why would this be happening? How can I prevent this so that all devices can pull an IP and connect to the internet?


  • is there any way to assign static DHCP addresses within the firewall? A static DHCP lease would make it so every time a particlar device sees a request from a given mac address, it will ALWAYS assign the same 'static' ip address to that device. That way you do not have devices grabbing 30-50 dynamic IP addresses. Usually you only want to set static leases on devices like servers, printers (things that are not likely to move, unlike laptops). Come up with an acceptable DHCP scope that can accommodate a number of dynamic addresses and a number of DHCP static leases. – Richie086 Mar 31 '14 at 20:45
  • Let me know if your firewall has this ability and give some additional details on your network range and what sorts of devices are on the subnet. – Richie086 Mar 31 '14 at 20:46
  • I have 8 devices with static addresses. I've set the DHCP range to be .21 thru .254, and reserve the .2 thru .20 addresses for statics. I assign the statics using the IP/MAC binding feature of the router, and there is no issue with these devices. This setup has been working for almost a year, and today is the first time that I've ever seen this glut of addresses by single devices. – aaaarrgh Mar 31 '14 at 21:01
  • The static IPs are a NAS, the switch, two WAPs, and a couple of servers that handle some inward-facing web-based services (continuous integration, a custom in-house test server, etc). The DHCP devices are a pretty even mix of Win7/8, MacOS, iOS and Android devices, along with two printers. – aaaarrgh Mar 31 '14 at 21:03
  • So, what what are the devices that are hogging the IP space? Laptops? Desktops? Maybe set the up as static leases to eliminate the problem – Richie086 Mar 31 '14 at 21:05

So if your firewall does support static DHCP leases, it would look something like this (ignore the network IPs, I just chose a class C range)enter image description here

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