I'm managing a Windows network with a Hyper-V cluster of three virtual hosts and around 25 virtual machines, one of which is a DHCP server. After taking over this setup a couple of years ago, I've found many misconfigurations and a lack of documentation. Recently, I noticed during a network issue that users lost connectivity when the DHCP server went down, likely due to lease expirations. I've implemented DHCP replication with a physical server to ensure redundancy, but even during cluster downtime, users still lost connections. My setup uses a 50-50 load balance with a 1-minute maximum client lead time, but I'm still unsure what might be causing these connectivity issues. Additionally, I've noticed that my server VLAN doesn't have a DHCP scope set up—should it?
5 Answers
Whether to have DHCP on your server VLAN is your choice! I usually prefer static IPs along with a DHCP range and reservations for known devices. By using a 50-50 load balance, you're not ensuring redundancy; instead, you're just balancing the load. For true failover, set it up so that one server is reserved as a hot spare while the other handles requests. Remember, having issues with DNS or other essential services while the cluster is down can cause further connectivity issues. Also, make sure to check lease times—if they're too short, clients needing renewal when the server is down can cause them to lose connectivity. Long lease times can help reduce load and ensure smoother operation. Lastly, document everything—your configurations, the reasoning behind them, and the choices you make, to avoid confusion in the future.
Ensure you have the IP helper addresses for both DHCP servers configured on every VLAN needing DHCP addresses, except for the VLAN where the servers reside. Also, I recommend keeping DHCP lease times at default or a more manageable figure like eight hours unless you're troubleshooting; this will help maintain stability during outages.
As for whether you need DHCP on your server VLAN, if you find it necessary, then yes, definitely set up a scope. Otherwise, you don’t need it. But do remember that the core issue here seems to be related to the failover setup, so ensure that's watertight.
Are you using DHCP helper addresses on your network devices so clients can find both DHCP servers? If your clients are on different VLANs, without those helper addresses, they won't be able to get a DHCP response.
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