Alright, here is the background.
Recently I was working on migrating a few locations off of bog standard Microsoft Windows DHCP server to Infoblox.
I'm no stranger to windows DHCP, but I've spent much more time with Infoblox over the past 6 years. And the majority of my time administrating windows DHCP was with the GUI.
Seeing as I was looking at a ton of scopes, I hate repetitive work, and I had a few locations that would need to be cut over. I figured this was a good of a time as any to work on my powershell skills.
In my case, all commands are displayed and used as if you are running them directly on the DHCP server itself. There are ways to run these commands on a remote system but I wont get into that here. Its trivial to update these examples for that use case.
First task, I want an easily readable export of the current scopes. Now there are two ways of doing this. What I did, was simply run
Get-DhcpServerv4Scope | Export-Csv DhcpExport.csv
Basically grabbing all of the v4 scopes on the server and throwing it into a CSV.
Recently I've learned that you can also do the following
Export-DhcpServer -File DhcpExport.csv
Okay cool, now no matter what method used for the above step the end result should be that we have a backup of the DHCP state before any changes are made.
In my personal example, I created a separate copy of this data, just labeled backup and exported to a "safe" location. After which I followed the sames steps but just used a different file name to create a working data set. Just really wanted to reduce the chance of accidentally modifying my "before" state data an having inaccurate data should I need to go back and troubleshoot an issue.
Next steps, Pre-cutover I want to reduce lease times for anything greater than one hour. The half life of your longest configured lease time will inform exactly when you want to make this change.
See section 4.4.5 of https://datatracker.ietf.org/doc/html/rfc2131
First, I need to find all the scopes where the current lease time is greater than one hour. No point in changing anything equal to or less than that.
Get-DhcpServerv4Scope | Where-Object {$_.LeaseDuration -gt (New-TimeSpan -Hours 1)} | Export-Csv -path Filename.csv
This one liner will grab all the IPv4 DHCP scopes on your server, filter for any scopes that meet our 1 hour criteria, then spit it all out into a CSV in this example just called Filename.csv
Now, you could manually review the csv, and for each scope reduce the lease time with the following command
Set-DhcpServerv4Scope -ScopeId x -LeaseDuration 1:00:00
Where x = scope ID
And if you find you only have a few scopes that need to be modified, this could totally be a good game plan, but in my case, and I think it would be safe to assume the majority of cases, lease times are typically 1 day or longer. So depending on the size of your environment you may be looking at a lot of copy/pasting
Besides, were already leveraging powershell, so lets make it do the boring work for us.
Get-DhcpServerv4Scope -ScopeId x
