I'm facing an issue with our DHCP server that's running out of available IP addresses for our scope (10.XXX.32.X). The DHCP scope ranges from 10.XXX.32.20 to 10.XXX.32.250, and the lease time is set to 8 days. Currently, we have a total of 231 addresses, with 213 in use and only 18 available. I've noticed one device with the same hostname has been assigned 20 different addresses but with different client IDs. Additionally, there are multiple registrations for two different Android devices with identical hostnames. Can anyone offer advice on how to resolve this or suggest a workaround?
4 Answers
It sounds like your lease time is way too long. Eight days is pretty extreme for today’s network, especially with so many mobile devices. I recommend shortening the lease time to something like 8 hours or even as low as 2 hours. This should free up your IP addresses and minimize the number of duplicate leases you see due to MAC randomization from devices like Android phones. The idea is to ensure that when a device leaves the network, its IP address can be reclaimed sooner rather than later. Also, try to look at the device causing the problem—often, this can be a device that randomizes its MAC address. It might help to disable that option for devices on your main network.
I’d say aim for a lease time of 4 hours, especially for guest networks. It reduces clutter and keeps things running smoothly.
Look into DHCP scavenging and check your settings. Too long of a lease time is often a recipe for disaster in busy networks and definitely leads to address exhaustion. Also, consider adjusting your DNS settings to match and ensure that it’s cleaning up old records to prevent any overlaps. You might also want to increase the size of your subnet to give you more available addresses if your network's growing.
That’s true—optimizing DNS and using proper scavenging should help, too. Don't forget, network size defines limits as well. Sometimes, just expanding the subnet can solve the issues fairly quickly.
Make sure to also scrutinize what's actually on the network. If you find out there are devices being imaged with the same MAC, that might also add to your problem.
The lease duration is likely causing you major headaches. Device MAC randomization is also something to watch out for. You see the same hostname getting different addresses mainly because the device is connecting with different MAC addresses. Have a look at the settings and see if you can turn off MAC randomization on those devices. For the DHCP setup, consider putting mobile devices on a separate VLAN with a shorter lease time, this will improve your overall management of IP addresses.
Yes, and when you do that, set a lease time of 1-2 hours for mobile devices. That way, IPs are clear and reduce conflicts.
Good point about separating devices by VLAN. It keeps the main network cleaner and everyone else better managed.
Definitely sounds like MAC randomization is the issue here, especially with those Android devices. Make sure people on the network are aware of the need to keep MAC randomization off for business devices. The recommendation of a 24-48 hour lease could really reduce problems. It gives devices a fresh lease and opens up those addresses put into use by devices that aren’t connected anymore.
Agreed! Just ensuring your policy is clear about device connections should also help with usage on your network.
You're spot on, keeping devices configured properly in terms of connectivity will save loads of headaches, especially with frequent users.
Exactly! Shortening the lease time will really help. By ensuring that the leases expire more frequently, you can reclaim IPs that belong to devices that are no longer on the network.