Why is DHCP not issuing all addresses in a scope?

Question

I have a DHCP server running Server 2019. My subnet is a /24 and the scope goes from .121 to .190. The appears to not be issuing address above .172 and also has a few addresses below that are not being issued as well (determined by looking at the leases). Looking at the statistics, it says I have a total of 170 addresses total with 116 in use (68%) and 54 available (31%). We regularly have issues with a PC or laptop not getting an address even though the statistics on the server show these numbers (within a couple of addresses) when this happens. Can someone tell me where I need to look to determine what the problem is?

Answer 1

Hello,

The issue you're facing might be due to various reasons. Here's a step-by-step guide to troubleshoot your DHCP server:

1. Open the DHCP management console and navigate to your DHCP scope. Look at the "Exclusions" tab. Ensure that there aren't any IP addresses in the range .121 to .190 listed here that are excluded from being assigned.
2. Check the lease duration settings. If it's set too high, devices may hold onto their leases even when they're not connected to the network, thus reducing the number of available IPs. To view or change lease duration, right-click on the scope > Properties > Scope tab > Lease duration.
3. Review reserved IP addresses. Reserved IPs will not be issued to other clients. Go to the scope, then click on the Reservations folder to see if there are any reservations for the unissued IPs.
4. Use the command ipconfig /release and ipconfig /renew on the affected client machines to check if there is an IP conflict with another device.
5. Make sure switches, routers, and firewalls are not blocking or rate-limiting DHCP traffic.

Best regards

Zunhui

Answer 2

1. there are no exclusions
2. I changed lease durations a while back as a troubleshooting step to 12 hours
3. we have no reserved IPs
4. we have used release and renew. It doesn't always work and I have not seen any addresses issued above .172 even though they are not shown as issued and there are a few addresses scattered lower that do not seem to get issued
5. this shouldn't be an issue. We have been able to get DHCP addresses at these network drops at times. If they were being blocked, we should never get DHCP traffic. We don't set rate-limiting

Answer 3

Hello Otis, did you solve the problem?

I have the same situation and I am thinking it could be a bug in the server 2019