How I (Finally) Found DHCP DNS Server Options (Without Losing My Mind)

Last updated on October 22nd, 2025 at 01:45 pm

Let me put it this way: I didn’t get DHCP DNS Server Options the first time someone tried to explain them to me. I nodded as if I understood and then spent the next three hours Googling “why don’t I get DNS on my devices” at 2 a.m.

Here’s what I learned after smashing (then fixing) my home network a few more times than I care to share.

What Exactly is DHCP Option 6?

So here’s the deal when your laptop connects to Wi-Fi, it doesn’t just receive an IP address. It also needs to know where it can find DNS servers. This is where DHCP Option 6 comes in, issuing DNS server IP addresses to your devices when they negotiate for an IP address.

I used to assume DHCP only handed out IPs. It also, turns out, is doing a lot more behind-the-scenes.

My First Real Configuration

So I thought I would install a DHCP on windows server for practice sake. Stared off simple-installed the role, made some kind of scope (that is just a range of IPs), and thought I was golden.

Devices connected. Got IPs. But couldn’t reach the internet.

I spent twenty minutes trying to figure out what was wrong, only to notice I didn’t set up Option 6. Rookie mistake.

DHCP Option 6 determines which DNS server is used by clients to resolve domain names. Without it, your devices are essentially blind they have an IP address but can’t connect to “google. com” into anything useful.

The Part That Actually Matters

This is what happens when you get your DHCP DNS options right:

The DORA Process (yes, really): Your host broadcasts a Discover request, the server responds with an Offer and offers up some IP and DNS config for you to use, your device then sends back a Request saying it accepts that offer, finally the server Acknowledges all of this and completes your setup including setting the correct DNS option.

It’s a handshake, but in four parts instead of one.

What I Wish I’d Known Earlier

Backup DNS Servers: You want to (and you should) have backup DNS servers set up. I got a lesson in this when my primary DNS server went down and took half of my network with it.” Now I never make less than two.

Option 15 Also Exists: DHCP Option 15 is the DNS domain name for clients, or alternatively “add this suffix to any hostnames”. Handy if you are running an internal domain.

Frequent Screwup Warning: Don’t get 6 confused with 5 (Name Servers) if you mix that one up your clients won’t receive the proper DNS server information. I’ve done this. It sucked.

The Security Items No One Discusses

So, after I read up on basic configuration I was reading about dhcp spoofing attacks where a rogue or malicious computer pretends to be your actual legitimate DHCP server and serves out fake DNS settings that points people to infected websites.

Sounds paranoid? Maybe. But enabling DHCP snooping on all of your managed switches and doing MAC address filtering takes like five minutes and will save you so much headache.

And When It Finally Goes Wrong recapCppTypeDefinitionClosing Down When Everything Goes Wrong

If it is reading ‘Expiry Date: No expiration Date’ then you probably have your DHCP service turned off, no addresses available in that scope and/or firewalls filtering UDP ports 67 and 68.

Half the time, it’s something dumb like the DHCP service don’t start. The other half it is a misconfigured scope or firewall rule you forgot about.

What I’d Do Differently Now

If I were to start again, I would reserve DHCP for the important hosts like servers and printers – best of both worlds How to do this in my environments DHCP (distributed) and use of reservations would be a win. Way better than having to deal with static IPs everywhere.

You can set up your dhcpd to handle Dynamic DNS updates as well, so hostname-to-IP mapping gets updated when a DHCP lease is assigned or renewed. Saves so much manual work.

The Bottom Line

DHCP DNS Server Options actually are not rocket science once you’ve configured them a handful of times. Yes, begin with Option 6 for DNS servers, toss in Option 15 if you require domain names and don’t skimp on old-school security.

Always test something on a small network. Trust me on this one.

The documentation makes it seem harder than it is. All you’re doing is saying to a device (be that an Amazon Echo or network switch) “here’s the DNS” and option 6 does just that.