it: UniFi Switch turns off if DHCP IP conflict

OK, I returned home after a few weeks and discovered for whatever reason that the DHCP server in my UniFi DreamMachine Pro had shuffled all the addresses. This means that my three servers are now conflicting because of two problems:

  1. I. have an old projector that is set to a fixed address of *.*.*.155 address and randomly one of the servers is right on top of this. The result is that the UniFi 24-port switch I have there disconnects. I’m guessing this is because I have multiple devices on there and it shuts it down.
  2. Synology wants the IP addresses of servers to remain stable. So while I can the .local domain which is using mDNS to find them or .localdomain which are the DNS records which Synology writes, in things like replication, it needs the real IP address

Solution: Set static IP addresses for the servers with DHCP Reservations

One strange thing about UniFi is that in the > Your machine > Settings > Networks > Default, you click on that entry and, you get the DHCP settings for your main network. The default is Auto-Scale Network which by default gives you *.*.1.1 as the UniFi Dream Machine Pro’s IP address, then is assigned *.*.*.2 as the honeypot address to catch network spam. Then you get 3, 4 and 5 as ones that you can assign that are completely free and any addresses that have not yet been assigned in the DHCP range. This is not that many. Note that you can use the automatically assigned range, but if there is a device already there you have to move it by changing its address temporarily and then assigning and blowing away the temporary assignment.

Note that if the device is not on, you can search for it in the Network > Client area and assign the new address, which will be picked up when the machine starts.

Note that UniFi unlike many systems doesn’t let you set the IP Range yourself.

How to force DHCP Renewals

OK, this is hard because DHCP has a lease period and you have to wait for the period to end for all this to happen, so you should manually reduce the lease time. Mine is set to 86400 seconds or 24 hours, so it will take a day for all this to happen.

So you either have to force a reboot or you can with Synology run a command line tp restart the DNS client but it is easier just to reboot.

Christie Projector has a static address

Ok, this is a 2009 projector but it did have LAN settings, what I didn’t realize is that it has had a static IP address of and all the time this wasn’t a problem because we never had an address land there. Then when one server got assigned, this caused mayhem with the UniFi switch disconnecting. So I just change this to one of the reserved addresses and also had the DHCP assignment there to make double sur.e

DNS name reservation

You can also reserve a specific name for this. The default is to take the name of the device and add a .localdomain for UniFi and a .local for mDNS

Synology Replication and Drive need updates

Since Synology uses IP addresses for thing like replication and the Synology drive, you have to change those as well. For replication this has to be done for each task, so takes some time.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

I’m Rich & Co.

Welcome to Tongfamily, our cozy corner of the internet dedicated to all things technology and interesting. Here, we invite you to join us on a journey of tips, tricks, and traps. Let’s get geeky!

Let’s connect