DHCP ISSUE, but configuring conflict detection attempts makes it go away (somewhat)

Question

I'm in a school environment with Windows DHCP/DNS servers. I've been having DHCP issues for quite a while. I've had a few vendors look into the issue, but no one can figure it out. When a client's lease expires it can sometimes take 10-20 minutes for the IP address to renew. I get calls about once a week that "half my class cannot connect to the internet". These are random classrooms, sometimes more than one at the same time, but never the entire building. My current lease time is set to 8 days. I've set the lease time shorter which made the issue more frequent. If I set the lease to three weeks, this spreads out the frequency of the issue.

Recently I noticed that if I enable conflict detection attempts in my DHCP server's IP4 settings the issue goes away (somewhat). I currently have this setting set to 1. My wireless controller still displays that clients are having issues though, "DHCP server is not responding to requests", but I'm not hearing any complaints from users. I few times every hour I receive a message like this from the wireless controller that a client or two are having issues and then the issue gets resolved a few minutes later.

Port mirror sessions and logs tell us that clients are having trouble connecting to the DHCP server when this issue is occurring but we cannot figure out why.

Answer 1

Hello @Andy Emerine

Considering that you had different experts already looking at the issue, it is safe assume that the issue is not related to the DHCP server, and performance on the DHCP (CPU, RAM, etc..) is correct, system updated, scopes, rules, and options are defined correctly and intermediate network is working fine.

In this case, I would suggest to look in the other direction: The clients. Since you are working with a school network, there is always the chance of some smart students poking here and there in the system. First I would check is if you have computers with static IP assigned from the DHCP pool. You can use the Get-NETIPCONFIGURATION cmdlet with the -CimSession swtich in order to retrieve information from remote computers. Reference:https://learn.microsoft.com/en-us/powershell/module/nettcpip/get-netipconfiguration?view=windowsserver2022-ps

On the other hand, it is possible that there could be some IP exhaustion due to use of virtul machines (for example in IT classrooms, etc..). If the virtual machines in a host are configured with Dynamic IP and they are granted External virtual network, they will pass the broadcast requests to the physical network DHCP.

As usual, also ensure that drivers and updates are installed in the Clients.

Last but not least, it may be just a network readiness at the moment of logon, for which you can try the next settings:

Set the policy to “Always Wait for the Network at Computer Startup and Logon” as Enabled
Policy path: "Computer Configuration \ Administrative Templates \ System \ Logon \ Always wait for the network at computer startup and logon"
Reference:https://learn.microsoft.com/en-us/previous-versions/windows/desktop/policy/logon-optimization

Hope this helps with your query,

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Answer 2

Here are a couple of issues I have discovered and resolved today. However I do not see any network improvement. Maybe it will take a few days to work itself out?

I ran netsh dhcp show server and the old DHCP server displayed in the list of authorized DHCP servers. I then ran netsh dhcp delete server oldservername oldserverIP to remove the old DHCP server.

An ipconfig /all on the DHCP server displays that it has two gateway addresses. The correct one and 0.0.0.0. The 0.0.0.0 address was listed at the top. I do not see this when using the UI, control panel/network & sharing center. I have removed the 0.0.0.0 address so that only the correct address is set.