When it comes to managing IP addresses, few of us would forget to track the IPs we assign manually to our WAN interfaces, servers, switches, and etc. However, once we decide to assign a DHCP scope to a subnet we tend to "set it and forget it". In many cases, this is a big mistake.
For those of us that have been around awhile, we can remember situations where DHCP wasn't available and we had to assign all of our users' IP addresses by hand. Wow did that suck. I remember having to have multiple IP address tracking spreadsheets in Excel because I had too many addresses to fit them all within the row limitations of the application. I think I must have memorized at least a few thousand of those address assignments and a few of them are still with me today.
Now that I have DHCP at my disposal I simply assign a scope for that subnet and I can pretty much forget about it. However, that would be missing an important step - the monitoring of that DHCP scope. DHCP scopes running out of addresses is a frustrating and time consuming ordeal. The users can't connect to the network so they call the helpdesk. Since they don't have an IP address the helpdesk person probably starts troubleshooting at layer 1 and works their way up the stack. Once they determine what the problem is, then the scope has to be widened which may result some devices needing to be readdressed. It's a headache and it's a waste of time.
The simple solution is to ensure that your IP Address Management solution includes the ability to monitor and alert on DHCP scope utilization. This way, you'll know before you have a problem and can proactively address the issue before the users or the helpdesk are impacted.
As of now, the new SolarWinds Orion IP Address Manager (IPAM) includes this functionality. These are key new features, monitoring and alerting on DHCP scope usage, and I'm extremely pleased to see them within the product so soon after the v1 release (the current release is 1.5). You can of course download a copy to try it out for yourself from SolarWinds.com, but regardless of which application you decide to deploy, remember to monitor those DHCP scopes...
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