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How to create and delete a DHCP reservation in Windows Server 2019

Sometimes you may need to reserve an IP address for a workstation or a device from your DHCP pool. Administrators can easily configure a DHCP reservation in their DHCP server when they need to reserve a permanent IP address. A DHCP reservation is a permanent IP address assignment. It is a specific IP address within a DHCP scope that is permanently reserved for leased use to a specific DHCP client. For more on DHCP Console Icons Reference .

Create and delete a DHCP reservation in Windows

Reservations are used for DHCP-enabled devices like print and file servers or other application servers that always have a fixed IP address on the network. A reservation consists of the following information.

For more information on DHCP , see the following links below – For more information on Automatic IP Assignment:  Dynamic Host Configuration Protocol  (DHCP) – How to install  Dynamic Host Configuration Protocol  on Windows Server 2019 – On how to configure DHCP:  Post-deployment of Dynamic Host Configuration Protocol . – How to configure DHCP Server option 60, 66 and 67 for Windows Deployment Services – Information on BOOTP Vendor Extensions and DHCP Options . – We can’t sign you with this credential because your domain isn’t available – Why Can’t I Connect with a 169.254 IP Address?

To configure a DHCP Reservation , follow the steps below. – The steps in configuring DHCP reservation in Windows Server 2019 is similar to other versions of Windows. – If you’ve heard of static IP addresses before, this is very similar. Since you manage it all from the DHCP Server.

Step 1: Open the DHCP Manger console from the Server Manager

This will open the DHCP console. In the console tree, Step 2: Click reservations

Right-Click on the reservation and – Click on New Reservation as shown below

Step 4: In the new reservation dialog box, provide the values for the following fields: – Reservation name. – IP address. – MAC address (without hyphens). – Description.

Under supported types, select one of the following options: – Both

When you have completed the details, in the new reservations dialog box, – Click on add and then on close.

To add another Reservation, follow the same procedure as shown above – You can add a lot of reservations as you want.

Now we have our serverations created as shown below

Verifying the DHCP Reservation (create and delete a DHCP reservation in Windows)

– For more information on these commands, see DNS Error: How to fix Err Connection Timed Out Error . On the Print Server, release the server IP address at the command prompt with the ipconfig/release command.

On the DHCP Server, from the DHCP console under address leases , verify that the reservation displays as inactive.

Furthermore, On the Print Server, renew the client’s IP address at the command prompt with the ipconfig/renew command.

On the DHCP Server, in the DHCP console under address leases, verify that the reservation displays as active.

Delete a Reservation – To delete a DHCP reservation, simply right-click on your desired reservation and hit the delete button

In the DHCP confirmation Windows, click on Yes

That is all that is required to create and delete a DHCP reservation.

I hope you found this blog post on how to create and delete a DHCP reservation in Windows helpful. Please let me know in the comment session if you have any questions.

Thank you for reading this post. Kindly share it with others.

• DHCP Reservation

A DHCP reservation is a permanent IP address assignment. It is a specific IP address within a DHCP scope that is permanently reserved for leased use to a specific DHCP client.

Users can configure a DHCP reservation in their DHCP server when they need to reserve a permanent IP address assignment. Reservations are used for DHCP enabled devices like print and file servers or other application servers that always have the fixed IP address on the network.

A reservation consists of the following information:

Working with DHCP Reservations in the Microsoft DHCP Server

Configuring a DHCP Reservation

• Open the DHCP console.
• In the console tree, click reservations.
• On the action menu, click new reservation.
• Reservation name.
• IP address.
• MAC address (without hyphens).
• Description.
• In the new reservations dialog box, click add then close.

Verifying the DHCP Reservation

• On the client computer, release the client’s IP address at the command prompt with the ipconfig/release command.
• On the server computer, in the DHCP console under address leases, verify that the reservation displays as inactive.
• On the client computer, renew the client’s IP address at command prompt with the ipconfig/renew command.
• On the server computer, in the DHCP console under address leases, verify that the reservation displays as active.

Client Verification

• To verify the client’s IP address, set obtain IP address automatically from TCP/IP properties.
• Use the ipconfig/all command. Verify that the DHCP server IP address for the partner network connection is the IP address of the DHCP server’s partner network connection.
• Use the ipconfig/release command to release the IP address from the DHCP server.
• Use the ipconfig/renew command to renew the IP address from DHCP server.

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• Routing Tables
• IP Address Conflict
• ICMP (Internet Control Message Protocol)
• Frame vs Packet
• What is PCAP?
• 192.168.1.245
• DHCP (Dynamic Host Configuration Protocol)
• IP (Internet Protocol)
• Routing Software
• 192.168.2.1 – What Are its Uses and Why is it Important?
• Broadcast Domain
• How to Find a LinkSys Router IP
• 127.0.0.1 – What Are its Uses and Why is it Important?
• What is a Zeroconf?
• How to Change an IP Address
• How Unix and Windows traceroutes differ
• 192.168.0.1 – What Are its Uses and Why is it Important?
• IP Address Classes
• Broadcast Address
• QoS (Quality of Service)
• How to Set a Static IP
• 192.168.1.1 – What Are its Uses and Why is it Important?
• What is an L2TP?
• NAT (Network Address Translation)
• Static Route
• Network Routers
• Collision Domain
• MPLS (Multi Protocol Label Switching)
• Subnet Masks
• What is NetBEUI?

• About the Authors

How to Reserve IP Address on Windows Server DHCP?

DHCP reservation allows you to reserve an IP address for a specific device by its physical (MAC) address. Such a device will receive the same IP address from the DHCP server, and it will never change. In this article, we’ll look at how to create and manage DHCP reservations on a Windows Server host.

Some devices on your network, which are used by other users and services (servers, printers, scanners, routers, switches, storage device, etc.), require a fixed static IP that should not change. There are two ways to assign a specific IP address to a device on a TCP/IP network:

• Manually set a static IP address in the device settings;
• Reserve an IP address for the device on the DHCP server.

The centralized reservation of IP addresses on the DHCP server allows you to manage the IP addresses of the devices on your network from a single console. There is also no need to log on to each device locally and manually set the IP parameters for the network adapter.

Adding DHCP Reservation on Windows Server

The Windows Server DHCP Server role is used to assign dynamic IP addresses to client devices.

Use the DHCP console to manage this role. You can run the console from System Manager > Tools > DHCP or by using the dhcpmgmt.msc command.

Assuming your DHCP server already has configured scopes for which you want to create IP reservations. Expand your IPv4 scope in the DHCP console where you want to create the reservation.

You can create a new DHCP reservation from any leased IP address or create a new entry manually.

If the DHCP server client has already received a dynamic IP address from your DHCP server, you can reserve this address.

• Expand the Address Leases section;
• Find the DHCP client you need in the list (currently issued dynamic IP addresses have a lease expiration date);

• The current IP address will be reserved for this device’s MAC address;
• In the Reservations section, a new entry will be created for your device.

You can also create a DHCP reservation manually. To do this, you will need to get the hardware (MAC) address of the device’s network adapter. On Windows you can find your MAC address with the command:

In this example, the Physical Address is 08-3E-8E-AA-F3-0D . Copy this value.

Right-click on the Reservations section in the DHCP console and select New Reservation .

Specify the new reservation settings:

• Reservation name : type the network name of the device;
• IP address : set the device’s IP address from your DHCP scope;
• MAC address : paste the physical adapter address you just got;
• Descriptions : provide a device (optional).

Click the Add button to create a new reservation.

If you entered the MAC address in the wrong format, an error will appear “The Unique Identifier you have entered may not be correct. Do you want to use this Identifier anyway?”. Double-check the MAC address in this case.

You will need to reboot your device to obtain a reserved IP address. Or run the following commands to release the old IP and get a new one from DHCP server.

You can manage your reserved IP addresses from in Reservation section. This is where you can delete or change any of the DHCP reservation settings.

Managing DHCP Reservations with PowerShell

You can also create, modify, and delete reservations on the DHCP server from the PowerShell command line.

The Add-DhcpServerv4Reservation cmdlet is used to create DHCP reservations.

The following command will reserve the leased IP address for a device that has already received an IP address from your DHCP server:

If you need to create a new DHCP reservation for a specific MAC address, use the command:

Hint . You can find out the MAC address on a Windows computer using the command: Get-NetIPConfiguration | select @{n=’ipv4address’;e={$_.ipv4address[0]}}, @{n=’macaddress’; e={$_.netadapter.macaddress}}

To create multiple DHCP reservations in bulk, create a CSV file containing the Scope ID, Client Name, MAC, and the required IP address:

Then run the command to create DHCP reservations for all devices in this file:

You can change DHCP reservation settings with Set-DhcpServerv4Reservation cmdlet. For example, you can replace the MAC address for a reservation:

In order to remove the specific DHCP reservation, run the command:

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The Tech Journal

Static ip vs dhcp reservation.

In the many years I’ve been providing IT Services , I’ve noticed that whenever taking over a customer from a competitor, or providing consulting services for a company that has IT staff, that I don’t see DHCP reservations being used all that frequently.

I wanted to write a post and create a video to discuss the comparison, when each should be used and the various case scenarios. I’m hoping my readers may provide their own input in the comments.

See below for the video, or read on for the blog post!

As an example: When a customer was purchasing a VoIP PBX, the PBX vendor get angry when I requested that it be configured for DHCP so that a DHCP reservation could be used, I advised I’d prefer this method so I could change the IP when needed for maintenance or network restructuring. They tried to convince me the IP will change on a DHCP Server and the port forwarding will stop working, because they simply had no idea of what a DHCP reservation was. Ultimately when the day came where I had to change the IP and firewall rules for the PBX, I had to log a support call with the vendor since I couldn’t change the IP myself (which resulted in delays, and costs). If we were using DHCP reservations, I could have simply modified the firewall rules, modified the IP address on the reservation, and restarted the device using the buttons on the front panel (I didn’t have any other access to the device).

Just to state the obvious:

• A static IP address is an IP address that’s manually set on a NIC (Network Interface Card).
• A DHCP Reservation is a pre-set IP that’s provided by a DHCP Server, and given to a NIC when a NIC calls out to a DHCP server for an IP address.

Static IP Addresses

It’s in my opinion that for server, network, core, and all top level infrastructure, all of these devices and services should be configured with Static IP addresses.

These devices which are almost always running, and have other services that rely on them, require a set static IP that should and will not change. Typically, these IP addresses will never change, even when major changes are being made to the core infrastructure.

These addresses should always be logged, documented, and added to network topology maps.

An example of devices commonly seen with Static IPS:

• Storage (SAN, NAS)
• Network Switches, Routers, Gateways, Load Balancers
• Wireless Access Points
• Computers/Workstations using special services (or requiring firewall exceptions)

DHCP Reservations

DHCP stands for Dynamic Host Configuration Protocol, and was created to dynamically configure hosts networking configuration on the fly for easy deployment.

In it’s most simplest explanation, when a computer (or device) that is configured to use DHCP reaches out to the network, the DHCP server will assign and provide an IP address for the computer to use.

In home networks, pretty much every computer and device will get it’s IP address from the DHCP server running on the router.

In business networks, pretty much every computer and device that isn’t hosting services will get it’s IP address from the DHCP server running on one of their servers or routers.

DHCP Servers support something called a “DHCP Reservation”, which essentially allows you to provide a pre-set IP address to a specific client based on it’s physical MAC address. This means that the device will always get the same IP address and it will never change (whereas they typically do on occasion).

I’m surprised I don’t see these used more often, as they can become quite the powerful tool on the IT tool belt when used properly. I’ve listed some pros and cons below.

• Manage IP addresses (IP reservations) from a single console
• Ability to change IP addresses on the fly easily from a single console without having to log in to the device.
• Manage network topology for ROBO (Remote Office, Branch Office) remotely, easily, and efficiently.
• Manage IP addresses for 3rd party devices that you don’t normally have access to modify (tell the vendor to set to DHCP), reducing support calls for external services.
• Ability to create different PXE boot environments as each reservation can have it’s own PXE boot options assigned.
• Device must support DHCP Configuration.
• The device MUST RELY on a DHCP Server once set to use DHCP. If the DHCP Server is down, so is the device.
• If rogue DHCP servers appear on your network, it may disrupt communication (this can also happen with static IPs and conflicts).

So with the list above, DHCP reservations look pretty powerful. The next question, is where do we use DHCP reservations. Let’s finish off with the devices we’d use them on, and what use case scenarios apply.

• 2nd Level (non core) Routers and Gateways
• IoT Devices
• IP PBX Systems (VoIP, Traditional with IP Management, etc).
• Thin Clients and Zero Clients
• Remote Offices (remote sites with limited access)
• Remote Support environments
• Branch Offices
• IP Phone Networks
• Wireless LAN Access Point VLANs

DHCP Reservation Use Cases

I use DHCP reservations frequently with customers that have remote or branch offices in remote geographical areas. When supporting these users and troubleshooting issues, it’s awesome to be able to just log in to the DHCP server to change IP addresses of printers, phones, and wireless access points.

Also, when configuring, shipping, and deploying new devices to these offices, I can simply log and write down the MAC address, configure the DHCP reservation, and the device will get the IP address I’ve chosen once it’s connected to the network and powered on.

Using DHCP reservations, you can easily make big changes to these remote networks without having to be present. If you were to use Static IPs and something was misconfigured, this might cause a physical visit to the site to resolve.

If by change a vendor directly dropships equipment to the remote site, I can simply call someone at that office to get the MAC address. Most devices with a NIC (printers, MFPs, wireless access points), all usually have their MAC addresses printed on the outside of the box. With this information provided, I can login to the remote server, create a DHCP reservation, configure drivers, and push the device config out to the network.

DHCP reservations add to the whole concept of a centrally managed environment, which further helps ease of maintaining, and supporting it.

Leave a comment and let me know your thoughts!

  49 Responses to “Static IP vs DHCP Reservation”

Very good information. Thanks for sharing.

Would you create a DHCP reservation for your network switches? I have about 15 –

Typically static IPs would be used for switches, as they would generally always need to be accessible, even when a DHCP server is down.

There might be a few odd non-standard use cases where non-backbone switches may use reservations in remote sites, but I could only see this ever being used in geographically remote sites that aren’t easy to visit.

Your explanations are so easy to follow.

Thank you for not assuming that we’re all IT professionals!

Hi Stephen,

So sorry to address you as “Kevin”…my bad. I had just read your reply to Kevin.

No problem Jerry! Cheers!

I’m trying to set up parental controls via a dns server. I realized that it was possible to get around the dns server by changing the dns server on each device. I’m trying to figure out how to force all devices on my network to go through the dns server I have chosen. I’ve come across port forwarding a few times but am struggling to nail down the steps to make it work. Could you possibly help me with this? Thanks in advance!

In Christ, Kenny Sparks

Thank you for the thorough, easily understandable explanation, Kevin.

I agree whole heatedly. It’s astonishing to think that any vendor supplying network equipment wouldn’t know DHCP. I’ve known about reservations for a long while, but it’s never really been showcased as a solution. Whatever makes our lives easier I always say.

This is fantastic info, but when you are a 3rd party vendor that has the only remote access to a device, static is best. It allows for NAT IP configs as well as other VPN server options the hospitals (in my case) use. In other cases, when a reservation or reservations aren’t documented properly, remote access becomes a problem when DNS and anything else is changed. Obviously this can happen with static as well, if the hospital doesn’t notify the 3rd party of the changes, however, this is generally, at least in my teams experience not the case. Hope that improves things.

I follow basic rules for when to use static IPs and DHCP reservations: 1) Router or Core switch – Static IP 2) Server – Static IP 3) All other infrastructure is DHCP w/reservations (switches, APs, printers, cameras, DVRs, time clocks, appliances, etc)

I contemplated using DHCP for most servers, but since DHCP servers have to be static and some applications might have problems if an IP changes unexpectedly (like due to a DHCP server failure or even a bad switch vLAN change), I decided to keep all servers static.

I’ve had many vendors tell me they don’t support DHCP, but 100% of the time they don’t understand DHCP w/reservations is effectively the same as a static IP. I’ve never come across a device connected to the network that doesn’t support DHCP even though I’ve been told by a vendor on multiple occasions their equipment doesn’t support it. I do not budge on this, and force them to learn their equipment better. I’m sure something exists out there that doesn’t support DHCP, but do I really want to use something with that bad of a network implementation? What else can’t it do?

The cons are minimal and can mostly be mitigated via a robust DHCP server infrastructure. 1) DHCP server must be available – Redundant DHCP Servers make this robust 2) Nothing can interfere with requests between client and server This one is obvious, but the only problem I’ve had in the past 15 years using DHCP reservations was our MPLS provider all of a sudden stopped passing DHCP requests from one site to our data center. The work-around was to install a local DHCP server with the reservations defined until the problem was resolved. Once the provider fixed the problem, I just re-pointed the routers to the data center DHCP servers again. 3) A rogue DHCP server can cause problems. It’s pretty quick to identify this is happening and doesn’t take long to find it. If you disable or isolate unused switch ports, then this has very little chance of happening.

It’s important your lease times are long enough to give you time to respond to DHCP server problems.

The pros are massive: 1) All IPs are authoritatively documented in DHCP (minus routers and servers). This makes managing the IP space so much easier. I put in dummy reservations for servers just so DHCP includes those as well. 2) There is almost no chance of an IP conflict 3) Infrastructure setup can be done in one location (like corporate) and moved to its final destination without any reconfiguration required. It’s convenient to setup switches, APs, and printers at corporate while on the network, and as soon as you plug them in at the remote location they just work (setup the IP reservation ahead of time). 4) Reconfiguration of IP scheme is trivial. I’ve done this many times to correct poor IP schemes I’ve inherited, and by setting the lease time to 5 minutes before the change, all devices pull new IP information almost immediately. If there’s a mistake on vLANing, the correct IP will be pulled in only a few minutes once fixed. When the project is complete, set the lease times back to normal values. 5) It’s trivial to replace a device because there will never be an IP conflict. Modify the IP reservation when it’s time for the new device to be installed, and the new device will take over the IP and the old device can still be connected if necessary as it will just pull a random IP at this point (or a set IP if you want to setup another reservation). 6) The IP scope range can be used more efficiently because IPs are managed centrally on the back-end, and it’s not reliant on devices being configured with the correct IP. I never have to guess what device has what IP and wonder if something was set to the wrong IP. I can look at my DHCP server to know what’s what. 7) If you need to make a default gateway change (either temporary or permanent), it’s trivial. This has come up before because we needed to change the destination of traffic outgoing from a location temporarily while service was being performed on the primary equipment. It’s an unusual event because normal redundancy usually addresses problems like this, but I’ve had larger failures to deal with that required temporary installations to cover until repairs to utility infrastructure is completed. Once the repair is done, updating the default gateway again gets everything flowing properly.

I’m an adamant supporter/enthusiast for DHCP reservations. 🙂

Ben, you’re awesome! Thanks for contributing to the discussion! Excellent advice!

Hi Steven, If a device has a static IP address should that address be included in the DHCP Scope, and then ‘dummy reserved’ out, or should the static IP address be outside the DHCP Server Scope? Say the network is not too big – can I set a scope of 192.168.1.2 to 192.168.1.99, then Fix the IP addresses of my Printers, Accesspoints etc into the 192.168.1.100 to 192.168.1.150 range, say, which won’t require any reservations as the fixed IP devices wont request IP addresses anyway, or should I Fix the IP addresses inside the scope, and just give them reservations, so no other device is accidentally given the address belonging to a fixed device. The advantage I see for the second method is that the connected devices all exist within the DHCP scope, and can be documented. Thanks for your article – just wondering about best practice – pros and cons of the two methods.

For best practice, I wouldn’t recommend using Static IPs inside of the DHCP pool range. For example, you’d want to have your DHCP range from .100 to .199 and then have your servers in .10 to .19 and printers from .20 to .30, etc… It just avoids problems…

As for DHCP reservations, you can have those within or outside of your DHCP scope.

Cheers, Stephen

This exercise asks you to create a DHCP reservation on the current scope, to ensure one of our servers will have the same IP assigned to it. Create a reservation on your DHCP server to ensure that one of your servers (for instance SRV02) will always have the same IP assigned to it. We want to assign ip 10.1.1.200, for instance Once you create the reservation print the output of the command: Get-DhcpServerv4Reservation -ComputerName “dhcp01” -IPAddress 10.1.1.200 | fl *, (the IP is merely for illustration purposes) kindly answer me asap.

[…] Static IP vs DHCP Reservation […]

Hi, is there a way to reserve a range of IP addresses for specific manufacturers? I have 15 Hickvision security cameras, currently configured for static IP. I would like to reserve a DHCP IP range on X.X.X.180-199. So I know the cameras will always be in this scope, by the same token I could have all my Apple devices in X.X.X.150-170 … etc.

MS best practice is to use Dual DHCP servers with either fail over or load balance and use DHCP reservations vs setting static IPs now for servers. The only thing you set static is core networking / hypervisors / routers

THANK YOU! It’s sadly “acceptable” to interchange these terms. I have to just cringe and let it go, I’ve even seen a router with a “Static DHCP” settings. wtf- static – dynamic, that’s really sad.

Could you explain what “hard wired” explicitly means?!? An RJ45 port – removable jack is not hard wired! A removable is not a hard wired connection… yet so many “tutorials” interchange these as well

I believe people just use the term “hard wired” in reference to a hardware wired network connection, versus something like wireless.

One subtle disagreement: You said “The device MUST RELY on a DHCP Server once set to use DHCP. If the DHCP Server is down, so is the device.” Not quite true, as many devices can utilize a self-assignment method for addresses when no static address is configured and the device is set for DHCP service. Windows calls this Automatic Private IP Addressing (APIPA). OS X also does the same thing (not sure what it’s called there).

APIPA addresses will be self-generated in the private IP range 169.254.0.0 to 169.254.255.255, with a subnet mask of 255.255.0.0

To the uninitiated, this can be very confusing and pointless. But it’s actually pretty cool because it allows the creation of ad-hoc networks: Just plug two (or more) computers into each other, and they will have a functioning network between them. Think file sharing here for example.

The other thing is a machine with a self-assigned address can easily be found on your LAN by using IPCONFIG, a scanner, or looking at ARP tables.

Self-assigned addresses are also noteworthy in that if your computer has one, it means it cannot find a viable DHCP server on your network,

Hey Joseph,

Thanks for the post with all the information!

Great post! I could not agree more with the position taken here. DHCP Reservation plays a huge role in effect network IT management and most importantly, network performance! Those not using this method of IP assignment are truly missing out and wasting time.

[…] Information on Static IP vs DHCP Reservation ( https://www.stephenwagner.com/2019/05/07/static-ip-vs-dhcp-reservation/ ) […]

I’ve been using DHCP reserved for years as a simple way to permit clients by MAC address and block all others.

Setting appropriate and reasonable DHCP lease times for mixed type of clients — such as an hour for short-term clients versus a week for others — is often not possible on the gateway / DHCP server.

Perhaps some routers permit different lease periods for DHCP reserved clients; but from my experience both true dynamic and reserved dynamic expire at the provided period.

In the last 5 years, the D-link Wireless routers Ive worked with — and possibly other brands — often fail when the DHCP lease period expires on the DSL or cable modem. Sometimes its works; sometimes it doesn’t. In many cases the Wireless router needs to be rebooted. Which causes a mess for the connected WiFi clients.

I’m curious why the D-link isn’t notified by the DHCP server and simply gets the same address again within MICROSECONDS. Or maybe it is and the actual issue is the WiFi router is failing it’s clients.

My actiontec centerylink router uses DHCP reservations and over time the accumulation of those reservations slowed up the internet from 40 mbps down to 7mbps. By clearing reservations 7 to 40 instantly. Thoughts? Maybe I should use static in my practice.

Technically the use of reservations should not effect your internet speed.

For everything other than an Active Directory Domain Controller, I prefer to set up servers with DHCP Reservations. As you outlined, it is easier to centrally manage services you want to provide to these systems (via DHCP Options), updating addresses for whatever reason, such as if network configs need to be changed (i.e. subnet / VLAN migrations), having a central record of addresses on the network, migrating services from one server to the other while keeping the same address, etc. Also, configuring HA DHCP (High Availability) allows me to keep everything configured and provide addressing services while I do a migration, upgrade, or in the event of a failure.

In the world of printer management, if a device fails and you are replacing it with the same hardware model, simply swapping out the MAC in the DHCP Reservation, print services easily migrate without having to figure out a printer UI.

On systems that support it, I will set a “fallback” IP in the event DHCP services fail for some reason.

All of that said, some networks that I help administrate have dedicated IT staffing and sometimes they desire statics. I think due to fear of having the network crash due to a DHCP server failure (again, HA is beneficial here) and they are not comfortable with leaving the “old” way of configuring services.

For network devices, I will have a Management interface / VLAN configured with a static in a large subnet (for example, a /16) as a default VLAN. This makes routes and ACLs easier to configure and allows me to access these devices without any server-based core network infrastructure services.

Great post, and I hope more people will begin adopting the simpler design of DHCP and reservations.

Thanks for the writeup . I had a follow-on question. I always struggle with hostname resolution within my router (att). Now any programs I use will resolve it just fine (typically Putty, WinSCP, etc, even at the command line. But being a techie, I like to know why the heck it’s not working. My experience says that by setting a reservation rather than static ip, you are still utilizing DHCP, but resolution happens with DNS. So Am I missing something?

So this is a tough one because it’s dependent on the setup, hardware, and software.

If the DHCP and DNS software is connected, then by creating a DHCP reservation, it may automatically create an A HOST record in DNS for the reservation. There’s also a chance it will create an accompanying reserve DNS entry as well.

Keep in mind this all depends on the router vendor, what DHCP and DNS servers they are using, and if they are integrated.

I could be wrong, but I think some routers also use a single service/daemon that actually provides both DHCP and DNS from a single service.

Hope this helps!

Hello Stephen,

i have a client who has two physical lan networks ,in two different locations ,with the same IP Range , interconnected with a fibre optic cable. The result being a single logical network with two routers both having DHCP servers enabled and having the same IP range. This is necessary, because if in any case the optic link fails both physical networks have to operate their own individual network\ systems without interruption. But the problem is there are IP conflicts, despite DHCP reservations for specific systems in the respective routers. Certain systems get an automatic IP within the 169.254.X.X range and fail to communicate. Also there are separate Internet Connections at both locations.

Is there a work around , while maintaining the routers in the two physical locations .

I have thought about using two different logical networks with static routes assigned, but am not sure about it working. will i able to ensure communication between systems on the two different networks, as if there are on the same lan network (All the computers are windows systems, there are also Tablets and mobiles connected via wifi). But here arises another problem both physical locations have thier own servers , and the custom designed softwares requires the servers have each have a static IP that falls in the same IP range 192.168.0.X . This was set by the firm that did the software.

is there any other alternative work around.

Thanks, Anselm

There’s a big flaw in your network design.

If you’re using switches at both locations, with a fiber cable connecting them, then you should have only 1 router. Technically you could have 2 routers and it would be sloppy, but you should only have 1 DHCP server per subnet. This is why you are getting IP conflicts.

You make the comment “This is necessary, because if in any case the optic link fails both physical networks have to operate their own individual network\ systems without interruption.”. This isn’t actually necessary.

The proper configuration would be to have 2 different subnets at each location, each with their own router and DHCP. Then, route the different subnets in both locations. This would avoid any issues, put the different physical networks on their own subnets, allow you to customize IP allocation (since you can have a DHCP server on each side), and is the proper design. It would also allow you to configure custom routes for each subnet so you can specific which location uses what internet connection.

Thanks for the advice on using two different subnets. One of my concerns in doing so, is would a user on a computer on one subnet be able to browse the shared drives/folders on a computer on the other subnet , without having to manually type the IP address of the target system( Network Discovery being turned on in all the systems). Is it necessary to use a VLan for this . or i can i avoid that.

If you’re using Active Directory and/or DNS, you shouldn’t have any issues with network shares, accessing them, using them, etc… Using multiple subnets with routers is standard practice because of the limitations of how many devices or computers you can have in a single subnet.

As for your question about using a VLAN, I’m not sure why you’d want to use one, but technically you could if you had the requirement. What I would recommend would be to configure a router and route the subnets.

My company has chosen to try and mitigate security by using up all of the DHCP addresses in the scope to only allow a couple of free DHCP leases to be grabbed. If a reservation exists with a specific IP address and someone adds a computer using a static IP address with the same IP as the reservation, there will be an IP conflict. Which one will win? Which computer gets access to the network and which one just gets an error message about IP conflict and doesn’t gain access?

What vulnerability are you trying to mitigate, I’m somewhat confused by your statement or what you’re trying to achieve?

As for your question, it depends on how it’s detected or forced. Normally the computer that’s connecting 2nd will notice the conflict and decide to back off, but this can be forced. Also, there’s nothing stopping anyone from just using a different static IP and accessing the network.

Yeah, it doesn’t make much sense to me either, but my boss seems to think this ensures that he knows what machines are on our network. I personally think that something like the Cisco Identity Services Engine would be the best way to go.

This would do absolutely nothing for security, and wouldn’t provide any visibility in to what devices are on the network. DHCP is only for providing client configuration, nothing as far as network access or security.

You’d need something else like NPS or the like, which would require authentication before granting access to the network.

By the way, thank you so much for getting back to me so quickly. I really do appreciate it.

Sincerely, Chris

hello good day Sir

question. How to know if any computer has reservated ip ? note: i can not check dhcp server because i dont have acesss , any suggestions? . only i know that computer does not have ip static because check NIC

thx in advance

sorry my english is bad

Cristal clear, great expalnation and examples. Thank you, Stephen!

May I know what is the different between DHCP Reservation (active) and Reservation (inactive)?

I would need to know the exact context, but I’m assuming that an inactive DHCP reservation, is a reservation that is configured, however the client hasn’t contacted the DHCP server to retrieve it.

Whereas an active DHCP reservation, is a reservation that is active because the DHCP client has connected and retrieved it.

In the last years I have seen many and many devices changing their mac address at some point, be it an iphone with “privacy feature” enabled, to set top boxes, ip cameras etc… in such cases reserved ip gets lost, devices are still present and working but on different addresses. It gets confusing at some point. I think manufacturers or software and firmware developers should not allow such mac spoofin so easily, they give for granted that MAC are not revelant to end users but that’s not true, even a small “smart” home with plugs, TVs, smart speakers lights etc… has its complex infrastructure based on fixes addresses.

so Best Practice, my understanding and please correct me if wrong…. 1. Create a DHCP Scope that does not include Core Switches, Servers, Gateways 2. Create reservations using MAC Addresses for Printers, WAP’s, VoIP phones, cameras, Core Desktops and anything else that may want static ip and is not core infrastructure. 3. Reservations can be inside or outside the DHCP Scope,

I have one newly installed device that I cannot Ping. Created Reservation as per instructed, and still cannot get this to “talk” through the network. This is a type of PA Gateway. Installers says its my network. Suggestion to troubleshoot to get the device to “talk” through the network? I have found no reset button.

I have been using this myself for a specific use case. 1. Many homeworkers are remoting using simple hardware, to leverage the real hardware in the office for heavy graphics work. 2. Masquerading can cause issues with multiple remotes at the same time with this software (especially with double nat) that works better using direct snat/dnat translation (currently 98% gigabit throughput via double nat via a gigabit WAN & LAN setup). 3. This is a home business where they have a home private use need, but also two business networks within, that need to be not only isolated form the public network but also from the private home network who have …guests…. shall we say. This required a double NAT setup, that was still remote capable.

For this I use a /16 network for the private use, but 2 /24 networks within for business use. This also necessitates its own business wifi AP as two vlans that needed to tunnel through that private network.

Anyway, to get to the point, I needed to ensure the heavy load PCs had not only dedicated IPs but SNAT/DNAT was directly associated with those IPs (always), that would be easy to manage/administer, but would never be given to anything else. Note that the remote software used, relies upon the establised/related aspect of the firewalls and internal instigation only, via an intermediary security service. That meant ‘static reservations ‘outside of’ the DHCPs auto allocation range’, but within the network scope of the /24 network that the DHCP server(s) could access/control. Where the firewalled /24 addresses are relayed to /16 addresses on the private network that is firewalled from the public network.

I was however browsing to see if ip reservations ‘outside’ of the dhcp auto range, was accepted/standard practice and ‘working as intended’ by DHCP. So, good stuff. Thanks.

A good point made here….. https://docs.netgate.com/pfsense/en/latest/services/dhcp/mappings-in-pools.html

I guess another way to look at it is the pass the buck problem. The installer, never input a static IP, relying upon a net admin configuring DHCP reservations. The net admin, never set a static mapping in the DHCP, expecting the intaller to manually set a static one. Thats where you get the meme about the word ‘ass-u-me’. If both are done, does it matter ? Is the device going to fail to get the expected address, that someone somewhere expected it to get, as long as at least one of the above done their job properly ? 😉

Thank you for this article; it and the comments have helped clarify my thinking for my homelab.

With regards what to DHCP reserve vs what to Static IP, I would say (& I’m running) use static IPs for everything the DNS/DHCP server depends on to get running, and everything else (after that) uses DHCP reservation.

So, if a network runs everything through the internet modem/router, that is the only device with a static IP.

If a network has a router plus a core switch, and the DNS/DHCP is run from the core switch, the router & the core switch use static IPs.

Or, if DNS/DHCP is run from pihole (or adguard etc), the router, core switch, and DNS/DHCP hardware server have static IPs.

(I could go on…)

Lastly, “document” the static IPs by duplicating their configuration in the DHCP reservation.

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Configuring Windows DHCP, Part 3: Creating DHCP Reservations

Aaron Rothstein · August 22, 2017 · 2 Comments

Need to mix the convenience of DHCP with the consistency of a static IP? Use a DHCP reservation, and create them with PowerShell.

DHCP reservations explained

DHCP empowers us to automatically assign IP addresses to clients while adhering to standardized rules (address space, lease duration, DNS servers, etc). For most clients, we typically don’t care what IP address the client ends up with on any given day, but for other devices consistently connected to the network, there are benefits to having the device get the same IP every time. A prime example that everyone can relate to is a printer. If you have the printer shared through a print server, the print server needs to be able to consistently talk to the printer on a known IP address.

“A  DHCP reservation  is a permanent IP address assignment. It is a specific IP address within a DHCP scope that is permanently reserved for leased use to a specific DHCP client” ( tech-faq.com ).

In the previous post we created DHCP scopes. Let’s see how we can use PowerShell to create a DHCP reservation within one of those scopes.

Creating a DHCP reservation using PowerShell

For this demo, we will reference a Brother HL-2270DW printer as the device for which we want to create a DHCP reservation. In order to create the reservation, we need the MAC address of the printer. Note that a device may have more than one MAC address, you will want to identify the MAC address for the interface you are connecting (wired or wireless).

The MAC address for my printer’s wired ethernet interface is 30055c077312. Given this information, I can use the PowerShell cmdlet  Add-DhcpServerv4Reservation :

You can see that the reservation was successfully created using Get-DhcpServerv4Reservation or by using the MMC snap-in.

Copy DHCP reservations from an existing Windows DHCP Server

If you are already using a Windows DHCP server in your environment but are migrating to a new DHCP server, you can use PowerShell to copy the configured DHCP reservations from your old server to your new server. This will eliminate a lot of manual reservation creation or per-reservation scripting. The following example assumes you a have already created matching scopes on the New DHCP server from the old DHCP server:

Next Steps: Use PowerShell DSC resources xDHCPServer

Up to this point, we have used interactive PowerShell cmdlets to install and configure our DHCP server. While this is certainly a legitimate approach, in my next post we will configure the same server using a DSC configuration.

Reader Interactions

October 13, 2020 at 9:15 am

We have 3 DHCP Servers, how do I specify which server to make the Reservation on? I need to do it on all 3 servers.

December 20, 2020 at 12:28 am

I think the best approach would be to create a CimSession for the DHCP server you want to run your commands against, then specify the session object using the -CimSession parameter.

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DHCP Reservation

Setting up a network for the first time can be confusing. There are so many settings and just making heads or tails out of everything can take hours. Even worse, your equipment may make it seem like everything is just plug and play, but when you’re almost set up, you find that nothing works as it should. One setting that you may have to manually tweak for your server is the DHCP reservation setting.

DHCP Reservations Simplified So, you may be wondering what exactly is a DHCP reservation and when would you ever need to use this. There are several different scenarios in which you would want to set a HDCP reservation.

In short, setting a DHCP reservation allows you to keep the same IP address for your computer or connected device. Your server computer needs a consistent IP address. You may want to set the same IP address for your wireless printer. Maybe you want to set up forwarding ports for gaming. These are just a few of the situations you’ll encounter when you need the same IP address consistently. Without DHCP reservations, your devices will get reassigned a new IP every time it’s rebooted, which can be a real pain. This is when it’s important to change your DHCP reservation settings.

Why Not Static IPs? Setting your DHCP reservation is very similar to using a static IP. However, there are a few differences. Your DHCP reservations are managed directly from your router. Also, these are easier to adjust and maintain than setting up static IPs for all of your devices. You won’t have to get an IT expert in to fix your DHCP reservations. In fact, with your user manual and a little bit of patience, you can get your network running smoothly in no time.

Setting Up Your DHCP Reservations Setting up these reservations shouldn’t be too much of a hassle, but since instructions vary by manufacturer, it may take a little bit of troubleshooting. However, in general, the instructions are fairly similar from router to router.

Most routers are equipped to set DHCP reservations right out of the box, but if not, this issue can be resolved by downloading updated firmware, which can be found at the website of your router manufacturer.

You can enter your router settings by typing your IP address into the navigation bar of your chosen browser. You can scan through the settings to find DHCP Reservation, which many also be under DHCP Static Lease.

You will need to have the computer or device’s MAC address on hand when setting your DHCP reservation. Under the settings, type out the MAC address for your chosen computer or device, followed by the IP address you would like to reserve. You can repeat this step for several devices. Make sure to save your settings.

If you find that your computer isn’t running on the IP address, you may need to enter commands to release and renew the IP through command prompts or by accessing system preferences. Once completed, your device or computer should be on its assigned network and will remain on that network, even when you reboot.

Resources http://lifehacker.com/5822605/how-to-set-up-dhcp-reservations-so-you-never-have-to-check-an-ip-address-again

http://www.tomshardware.com/faq/id-1932491/difference-dhcp-reservation-dhcp-exclusion.html

http://www.linksys.com/us/support-article?articleNum=137180

• Help Center

DHCP Reservations - 5 Reasons You Need to Assign a Permanent Address to Devices on Your Network

Every device on your home network has a unique IP address. When your network is small you don't really have to think about these IP addresses. Your router takes care of managing them for you, giving every new device an IP address whenever it connects. In a small network, this is usually fine, and it is the way most people's home network runs.

As your network grows, managing devices becomes more of a task. Perhaps you want to set up a port forward to access something on your network from the outside. Or maybe you are interested in home automation and want to control various devices with custom software such as Home Assistant. Maybe you are just tired of always having to look up the IP address of a security camera in order to check its feed.

Once a network becomes large it can be hard to track down which device is which. Imagine having dozens of smart switches installed in your house on your network, each of them with its own IP address, and you have no idea how your IP addresses have been assigned. The sooner you start keeping track of your devices, the better. Don't wait until you have 100 devices on your network and you don't know where any of them are (by where we mean their IP address, not their physical location.)

Using DHCP reservations in your router: lets you manage your devices from one place, fixes networking problems that you didn't even know you had, is easier than setting up static IP addresses in each device, makes your network more reliable for port forwarding, and creates permanent addresses that are needed for home automation, gaming, and VMs.

Reason #1: DHCP Reservations: Manage All Your Devices From One Place

DHCP Reservations are created in your router. When you need to manage your devices it is easiest if they can be accessed through your router. The alternative is to log in to or access each device separately. This usually involves multiple passwords and interfaces and can quickly become quite complicated.

Once you have DHCP reservations set up in your router it is easy to not only find which device is which but also to change which IP address is assigned to each device. This type of micromanagement can be useful when tackling more adventurous networking topics such as home automation and port forwarding.

What are DHCP reservations?

A DHCP reservation is an entry in your router that assigns a permanent IP address to a device on your network. Every time that device is connected to your network it is guaranteed to get the same IP address. This is different than a standard DHCP IP address, which can change every time a device is rebooted or connected to your network. DHCP reservations are managed in your router, not in your devices. This makes managing your network easier because you only have to log in to one device (your router) in order to change the IP addresses on your network.

How do DHCP reservations work?

DHCP reservations work on top of the DHCP protocol, which is implemented inside your router. When a device connects to your network it sends out a special packet called a DHCP broadcast which only your router responds to. The router's response instructs the device to use a specific IP address.

In order for a router's answer to make it to the device, it has to have a way of talking to that device (before the device even has an IP address.) This is done using a low-level unique serial number that is permanently hard-coded into each device called a MAC address.

What is a MAC address? Every device on a network has a unique serial number permanently burned into it at the factory called a MAC address . MAC, or Media Access Control, is used to communicate on an IP network even before a device has an IP address. MAC addresses do not change (except in some rare cases such as virtual machines and software access points.)

Only the device with the MAC address that sent the request will receive the router's reply and assign itself the unique IP address that the router has told it to use.

Since a router sends its reply to a MAC address, it is possible to have the router always send the same reply to the same MAC address. This is what a DHCP reservation is. It is an instruction in the router to always send the same IP address to a certain MAC address. DHCP reservations are done by MAC address.

Some routers will hide the fact that you are dealing with a MAC address by giving the device a name. If you can favor making the reservation by MAC address you should.

Reason #2: DHCP Reservations Fix Networking Problems

Especially in Windows networking, every device on your network has the possibility of having a human recognizable name. Some people like to name their computer something memorable or funny, or other times a media server will be assigned a name so that it shows up in the client app. Also, many home automation devices automatically assign themselves a name that is a mash-up of the manufacturer's name and the device model number. While these names can be convenient, they can also be problematic to use, especially in a network that is susceptible to communication hiccups such as Wi-Fi.

In a Wi-Fi network with a spotty connection, it is frequently more reliable to use the IP address of a device than the name. This is because it reduces network traffic by not requiring an additional round trip of packets to translate a given name to its assigned IP address. It can be much faster to simply access a device by its IP address in an unstable network.

Many times you can ping a device by name and notice a small delay before the first reply comes back. This is the name resolution phase and it is completely bypassed by just using the device's IP address directly.

Of course, you could skip the name resolution phase with a dynamic IP address as well, but you don't know what the device's IP address is. This is solved with a DHCP reservation which makes the IP address permanent.

Reason #3: Using DHCP Reservations Is Better Than Setting Static IP Addresses

Using DHCP reservations to assign fixed IP addresses is a great improvement over the manual method of managing static IP addresses. In the early days, home routers didn't support DHCP reservations because they did not have enough RAM to keep track of all the devices. Instead, a static IP address had to be set up on devices that needed to have the same IP address whenever they connected to the network. This required finding each device on your network, logging into that device using its username and password, and figuring out its network settings.

Furthermore, you had to keep track of which IP address you had assigned to each device manually in order to avoid an IP address conflict. It was truly tedious and cumbersome and prone to human error.

DHCP reservation vs. static IP

With DHCP (Dynamic Host Configuration Protocol) you cannot always be sure which IP address each device has unless you have gone through the tedious chore of logging in to each device and assigning it a static IP address.

There is a better way. With DHCP reservations, you get to control which IP address each device gets, and you do not even have to log in to that device. This allows you to take control of your network and manage which devices have a permanent IP address all from the convenience of your router's admin interface.

Using DHCP reservations consolidates device management to a single point of maintenance. You can do it all in your router instead of having to sign in to each device separately. Most routers will not allow you to accidentally create an IP address conflict, and you do not need to log in to any of your devices.

Reason #4: DHCP Reservations Make Your Network More Reliable for Port Forwarding

When you set up a port forward you are pointing a port at an IP address on your network. At the time you set up that port forward, you should know what device is using that IP address. It would be extra nice if that device's IP address never changed. If you reboot your device and it gets a new IP address then your port forward will stop working and you may not realize why.

A device that is the target of a port forward needs to have a permanent IP address. You can either log into that device and configure its network settings manually or you can set up a DHCP reservation for that device in your router. Either of these will give that device a permanent IP address and keep that port forward working through reboots.

Should I use a DHCP Reservation?

When you want your device to get the same IP address every time it connects to your network, you should create a DHCP reservation for the device. It's easier, faster, and less prone to human error than attempting to manage static IP addresses on your network.

There are no negative side effects to a DHCP reservation and many positive benefits. If you are thinking about using DHCP reservations on your network, then you should definitely get started right away.

Reason #5: DHCP Reservations Are Needed for Home Automation, Gaming and VMs

When it comes to networking, some of the more common uses for DHCP reservations are gaming, home automation, and virtual machines. The process for setting up a DHCP reservation is the same for each of these topics, and each of them has its own unique set of benefits.

Is a reserved IP good for gaming?

Many games benefit greatly from a port forward. Multiplayer games that have a lobby usually pick one of the players as the lobby host. It's usually the player with the lowest ping lag who also has a port forward. The lobby host tends to get a better response from the game engine and as a result can get a significantly better score than non-host players.

Setting up a port forward to your game can decrease your lag to the game server. It is one of the first steps you should try when you are having performance issues with online multiplayer games. See our How To Port Forward Games guide for detailed instructions on this topic.

Before you set up a port forward, the device that you are gaming on needs to have a permanent IP address. You can either set up a static IP address on the device or a DHCP reservation in your router. Of course, we prefer a DHCP reservation in your router.

Why DHCP reservations are important for home automation

For basic home automation like the popular hubs and integrated switches, a DHCP reservation is not necessary. As soon as you try to use something fancier such as Home Assistant you are going to quickly bump into some of the annoyances of dynamic IP addresses. Some of the open-source interfaces to popular home automation platforms expect a device's IP address to be unchanging.

A common symptom is when a device is discovered, it works fine, but weeks or months later it stops responding to home automation software. This very famously happened with Home Assistant and TP-Link Kasa. Since Kasa devices do not allow you to control their network settings, you are forced to use DHCP, but the open-source Kasa interface does not play well with dynamic IP addresses.

It is a simple solution to log into your router and assign a DHCP reservation to each of your smart switches, smart bulbs, and smart hubs. After doing this you will notice significantly fewer communication disruptions.

DHCP reservations and virtual machines

Virtual machines are becoming more and more popular. They are useful for running old versions of Windows, testing software before installing it, simulating old arcade cabinets, and isolating potentially dangerous programs.

All of the virtual machine platforms such as Hyper-V, Proxmox, KVM, and VirtualBox allow you to specify the MAC address of the virtual network card assigned to each of your VMs. This is super convenient because it allows you to assign an IP address to a VM before you even boot it up for the first time. This allows you to control which IP address a VM uses when pulling updates during the installation process. It also makes it much easier to connect to the VM remotely using SSH, RDP, or VNC.

How to Make a DHCP Reservation In Your Router

Remember that you are reserving the IP address that the device should have every time it connects to your network. It does not necessarily have to be the IP address that it got automatically. Feel free to come up with any sort of numbering scheme that makes sense to you. For instance, you might make all cell phones be in the .50 range and all gaming consoles in the .80 range. It's up to you how you allocate IP addresses on your network. It's best to avoid .1, .100, and .255 though because they frequently cause conflicts.

After a DHCP reservation is created for a device, you will need to reboot the device if you assigned it an IP address that is different from the one it got automatically. Depending on the device, you will need to either push the reset button on the device, cyle power to it by turning a breaker off and then on, or wait until the device times out and reboots itself before the new reservation will take effect.

Step 1: Log in to your router

DHCP reservations are created in your router so to be able to make one you need to be able to log into your router. If you are not sure how to log into your router see our Login Guides .

Step 2: Find the DHCP section

After you log in to your router, look for the DHCP section. Sometimes it is in the advanced section and sometimes it is in the networking section. You might also find it in the LAN section, but it definitely will not be in the WAN section.

Step 3: Find the device on your network

Once you find the DHCP section, you should see a list of all the devices on your network that currently have an IP address. It may list the device name, the device IP address, or the device MAC address.

Something that might make finding a device on your network easier is to know that the first half of a MAC address corresponds to the manufacturer of the network adapter in that device. For instance, if you are looking for a PlayStation, you might find that your router has labeled it Sony. Or if you are looking for an Xbox, it might show up as Microsoft. There are numerous MAC address lookup engines on the internet that can help you figure out which MAC address belongs to which device. If you are worried about privacy, you only need to include the first half of the MAC address in search. Also, when looking up MAC addresses by vendor, it might be labeled OUI instead of MAC.

On a large network with a lot of devices, it can be hard to figure out which device is which. This is why it is easier to start DHCP reservations when your network is small.

Step 4: Reserve an IP address for the device

Once you have found the device that you want to create a reservation for look for a button or a link that says either assign or make permanent. When you choose that option, your router creates an entry in its DHCP reservation table. You should be able to see the DHCP reservation table in the router's web interface. Usually, the DHCP reservation table is where you modify and delete reservations as well.

Note that if your router allows you to make a reservation by name or MAC address we recommend making reservations by MAC address.

The larger your network gets, the more you are going to wish you started making DHCP reservations years ago. If your current router doesn't support DHCP reservations then you have a great excuse to upgrade your router now.

For answers to your networking questions, visit our Networking Help Center .

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Configure DHCP Reservations

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In this lecture, we are going to learn how to create a DHCP Reservation. We are going to create a reservation for our Windows 10 workstation with an IP address of 192.168.0.113.

In order to create the DHCP reservation, we would need to have our Domain Controller and our Windows 10 VM powered on.

The first step is to grab the MAC Address from our Windows 10 workstation and then we will be ready to create the reservation on our DHCP Server which is ITFDC01. Next, we will configure the Windows 10 VM to use DHCP for our second networking adapter and see if we grab the IP Address we reserved for it.

Start by logging in to Windows 10 VM. Open Command Prompt by clicking the Windows button and search for cmd.

Start Command Prompt by selecting it from the list.

We can grab the MAC Address of our VM by typing the getmac command.

Notice there are two MAC addresses presented. This is because we are using two network adapters. We can figure out which MAC address belongs to each network adapter by looking at the advanced settings of our VM networking configuration.

On the VM window, click Machine and Settings...

Click the Network tab and select Adapter 2. Expand the Advanced drop-down list and look for the MAC Address. 

Now we can see that the MAC Address listed here is similar to the second MAC Address listed in the command prompt. This is the MAC Address we will use to create the DHCP reservation because this is the MAC Address of the networking adapter that is attached to the same Host-Only network that our Domain Controller is using. Click OK to close the Settings… window.

Now, switch over to our DHCP Server which is ITFDC01, and open the DHCP Management console by opening Server Manager and selecting Tools and DHCP.

Expand our server, expand the IPv4 node and our Scope, and right-click on Reservations and choose New Reservation… 

For the Reservation name, we are going to enter the computer name ITFWS001.

For the IP Address, we are going to enter the IP Address we want our computer to receive which will be 192.168.0.113.

For the MAC Address, we are going to enter the MAC Address that we got from the Windows 10 workstation by entering the getmac command which is 08-00-27-70-AB-B4.

For the Description, we are going to enter ITF Workstation 001.

For the Supported types, we are going to leave the default radio buttons selected Both selected.

Click the Add button and then click Close.

TIP: You might be wondering what a BOOTP is. BOOTP or Bootstrap Protocol was designed to dynamically assign IP Addresses when computers boot up or are powered on. BOOTP is also capable of pointing the client computer to an image file containing Operating Systems. Unlike DHCP, BOOTP can only configure TCP/IP settings when a client computer is booted and not when it has already been booted to Windows or while it is up and running at the Desktop.

We can now see the new Reservation listed.

If we Right Click on the new Reservation we can configure the Reservation, Delete it or configure its Properties.

You can also double click on the Reservation and see the settings for the Router, DNS Servers, and DNS Domain Name.

Note that we cannot configure the settings in the middle pane when double-clicking the options displayed as a warning message will pop up.

You can change them by Right-Clicking on the Reservation and selecting Configure Options…

The Reservation Options window will appear.

Let's switch over to our Windows 10 VM and switch the IP Configuration to DHCP to see if it grabs the new IP Address settings we’ve reserved for it.

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Configuring DHCP Reservations

DHCP Reservations provide a way to reserve a particular IP address for a specific client, which is useful for clients that always need to have the same address.Why not just assign a static IP instead? You could, but then the client would not be able to get other configuration options (DNS server, default gateway, etc.) from the DHCP server if/when those options change—you would have to change them manually on every statically assigned computer.

Reservations are treated a bit differently than the other types of DHCP options, because an administrator must manually set up each reservation separately with predefined information from the client machine's network interface card. Aside from User and Vendor classes, client reservations are the most specific type of setting for assigning IP addresses to clients. To set up a reservation, follow these steps:

1. Expand the nodes for the DHCP Server and Scope in the DHCP MMC console.

2. Right-click Reservations.

3. Select New Reservation to display the New Reservation configuration box shown in Figure 3.27.

Figure 3.27 Configuring a Client Reservation

The options that need to be entered into a DHCP reservation are as follows (only the ones followed by asterisks are required):

■ Reservation Name* Uniquely identifies the client you are reserving

■ IP Address* A reserved IP address from the range of IPs in the scope

■ MAC Address* The Media Access Control number of the client's NIC

■ Description An administrative description to better identify this client

The Supported types configuration boxes refer to the method in which each client obtains DHCP information. Although most Microsoft clients will use DHCP only, Windows 2000 Remote Installation Services (RIS) clients use the BOOTP protocol to initialize. Older non-Microsoft clients may use the BOOTP protocol, so unless you are sure, it is probably safe to leave the default of Both selected.

Continue reading here: Configuring Bootp Tables

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Related Posts

• User and Vendor Class Options
• How DHCP Server Scope and Reserved Client Options Are Applied
• Using dns Dynamic Update Credentials
• DHCP Administrators Group
• DNSUpdate Proxy Group - Network Infrastructure Windows Server 2003
• Configuring Multicast Scopes

Readers' Questions

What are dhcp reservations?

DHCP reservations are static IP address assignments within a DHCP scope. This allows a particular device to be assigned the same IP address each time it connects to the network, making it easier for administrators to manage the network and for other devices to connect to the reserved device.

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• 27 Jul 2023
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Using Host Reservations in Kea

• Updated on 27 Jul 2023

The instructions in this article apply to features in the 1.8.X branch of Kea DHCP. The behaviors described have changed in the 1.9 branch: more flexible configuration options were introduced called "reservations-global" , "reservations-in-subnet" and "reservations-out-of-pool" to replace the old "reservation-mode" parameter.

• What is a Host Reservation?

The "host" in "host reservation" is a device that is interested in DHCP services, commonly a DHCP client or, with explicit configuration, a DHCP relay agent. "Host" and "client" can be used interchangeably most of the time. The "reservation" is an assignment of resources for the host, which can include an IP address, an IPv6 prefix, multiple IPv6 addresses, or any of a number of options.

Host reservations are also known as "address reservations," for their ability to reserve addresses for hosts, or as "static reservations," for their ability to override dynamic allocation from the address pool. In Kea terminology, we refer to them as "host reservations."

• When should you use host reservations?
• Example configurations
• Defining host reservations
• Performance considerations
• Migrating from ISC DHCP to Kea
• Host reservations can provide a pre-determined, unchanging address or prefix for a host. For example, a client that has special access (e.g., a firewall rule permitting access based on the originating IP address) needs to keep its address permitted in the firewall configuration. Another use case is that of a device with a mission-critical network service which needs to be accessible by IP address in case DNS lookups by name fail.
• Host reservations also allow you to provide consistent DHCP options to a host asking for them in an Option Request Option (ORO). You might learn over time that some devices in your network require a specific option in order to function correctly. Another example is associating the correct boot file with a host in the host reservation.
• Host reservations are useful when you need a static hostname for your host, such as for a server or application that is commonly accessed via domain name.
• They are also useful when you want to assign a client class to a packet to identify the device it's coming from, to further control subnet selection, lease allocation, hook functionality, etc.

A host reservation configuration consists of the criterion for identifying the client or host, followed by a list of reserved resources.

The host is identified in the host reservation through one of the following:

• client-id (v4 only)
• circuit-id (v4 only)

Reserved resources can include any of the following:

• prefixes (v6 only)
• option-data
• client-classes
• boot-file-name (v4 only)
• next-server (v4 only)
• server-hostname (v4 only)

Following is a basic example of a host reservation statement.

Example: host identifier

In this example, the host is identified by the device unique identifier (DUID) or duid . Alternatives are hw-address and flex-id . For DHCPv4 only, there are also client-id and circuit-id . Note: you can't specify more than one identifier for any single reservation, but you may have different identifier types over the span of multiple reservations.

The host identifier acts as a filter, telling Kea which identifiers to evaluate. If you only want hosts to be matched by DUID and hardware address, you can achieve this through host-reservation-identifiers: [duid, hw-address] . For best performance, have as few entries as possible; if you don't specify one or more identifiers, then Kea has to search for a possible host reservation using all possible client identifier types, every time it receives a new client request.

Example: addresses & prefixes

The reserved resources follow the host identifier. Every host reservation must reserve at least one resource; if not, Kea complains at configure time. Resources include address, prefixes, options, hostname, and client classes.

In this example, the host is assigned an IPv6 address as well as an IPv6 prefix. These are returned to the host in the IAAddr and IAPrefix options in the response from Kea.

More on this in the Kea Administrator Reference Manual (ARM) .

Example: options

Options are reserved through option-data . In this example, the DHCPv6 option with code 17, named OPTION_VENDOR_OPTS, is used to let the host know what vendor the server is hosted on: specifically, enterprise ID 4491.

Options specified in the host reservation are provided ONLY if requested by the host. For custom options, i.e., all those outside the defined standard list ( DHCPv4 , DHCPv6 ), a matching option-def must be included in the global Kea configuration, in addition to the option value specified in the host reservation. This is explained in the Kea ARM .

Options defined at the host level have the highest priority. In other words, if there are options defined with the same type on global, subnet, class, and host levels, the most-specific values, which are those at the host level, are used.

Example: hostname

The hostname resource is requested by a DHCP client containing DHCPv6 option code 39 OPTION_CLIENT_FQDN, or DHCPv4 option code 12 OPTION_HOSTNAME. Kea then mirrors the option in the response, but with the configured value. A DNS client is then able to use this information to assign the host to an A record. More on this in the Kea ARM .

Example: classification

A host reservation can also assign client classes, which is like a tag associated with a client. You tag the packet with the client-class so that it can then be used as an additional identification criterion in subnet selection, lease allocation, hook functionality, etc.

Read more on this in the Kea ARM .

There are three additional fields that can be reserved for the server to complete in responses under the DHCPv4 packet header:

• boot-file-name for the file field
• next-server for the siaddr field
• server-hostname for the sname field

Kea supports defining host reservations (HRs) in the main Kea configuration file, as described above, or in a separate database. If you are establishing only a few host reservations, the overhead of setting up an external database is probably not worth the effort; if you have hundreds of host reservations, they can be easier to maintain in a database.

It is possible to specify HRs in BOTH the configuration file and an external database. In this case, HRs in the configuration file always have precedence over database HRs, regardless of where in the config file they are specified.

Host Reservations in the Configuration file

Host reservation in the Kea configuration file are read at server start and kept in memory. There are three places (specified here in jq filter notation) in the configuration file where reservations can be defined:

• Global: .Dhcp[46].reservations
• Subnet-level: .Dhcp[46].subnet[46][].reservations
• Shared-network subnet-level: .Dhcp[46]["shared-networks"][].subnet[46][].reservations

Where in the file to put the host reservation configuration is an important decision. The location determines what portion of the network topology is served.

A global reservation can be used to assign certain parameters, such as a hostname or other dedicated, host-specific options, to any client, regardless of that client's location in the network. This is specifically useful for mobile or roaming clients.

It is also possible to assign addresses in a global reservation. This is enabled for corner cases, but it is generally a bad idea, because the address assigned may be unsuitable for the place in the network that the client has roamed to. (For example, the default gateway may be unreachable for that client.) Be aware that the global setting is a server-level configuration setting that excludes in-subnet reservations. You must choose either global or non-global reservations. This is the purpose of the reservation-mode setting.

Reservation mode

Just as reservations can be defined in different places, the reservation-mode setting can be specified in multiple locations in the configuration:

• Global: .Dhcp[46][reservation-mode]
• Shared-network-level: .Dhcp[46][shared-networks][][reservation-mode]
• Subnet-level: .Dhcp[46].subnet[46][][reservation-mode]
• Shared-network subnet-level: .Dhcp[46][shared-networks][].subnet[46][][reservation-mode]

The effect is local to the specific configuration portion, so a subnet-level reservation-mode only affects the subnet. When there are multiple reservation-modes specified, the one most specific to the matched subnet is taken into account. Thus, the global reservation-mode has the least precedence.

Here are the possible values for reservation-mode :

• disabled - this is a simple, straightforward switch to disable host reservations altogether. As Kea skips checking for reservations, the server may operate faster in this mode.
• all - this enables both in-pool and out-of-pool host reservation types. This setting is the default value, and is the safest and most flexible. However, since Kea does the maximum number of checks for reservations, it is also the slowest. It does not check against global reservations.
• out-of-pool - this allows only out-of-pool host reservations. With this setting in place, the server assumes that all host reservations are for addresses that do not belong to the dynamic pool. Therefore, it can skip the reservation checks when dealing with in-pool addresses, thus improving performance. Do not use this mode if any reservations use in-pool addresses. Caution is advised when using this setting; Kea does not sanity-check the reservations against reservation-mode and misconfiguration may cause problems.
• global - this allows only global host reservations. With this setting in place, the server searches for reservations for a client only among the defined global reservations. If an address is specified, the server skips additional reservation checks, thus improving performance. Caution is advised when using this setting; Kea does not sanity-check global reservations and it is possible to specify an address in a global reservation that is unreachable or unsuitable for the client.

If not specified in the configuration file, reservation-mode defaults to all .

When set to out-of-pool or all , global reservations are ignored. all causes the allocation engine to search for subnet reservations while verifying that the reserved address or prefix is not leased by another client. out-of-pool optimizes performance by leaving out the verification and should only be used if you are certain that reserved addresses/prefixes don't overlap with defined pools.

Kea doesn't allow both global and in-subnet reservations in order to simplify the logic for parsing the configuration file which reduces the processing required. Kea warns you at configure time if you have overlapping subnets or shared-networks, to prevent conflicts, and reservations are also checked for overlap with pools in their subnet. But there could theoretically be two reservations for the same host between global reservations and shared-network/subnet-level reservations. To check this would require evaluating the entire configuration twice for every client request, which would be very inefficient.

Since Kea versions 1.9.1 and 2.0.0, the new flags named "reservations-global" , "reservations-in-subnet" and "reservations-out-of-pool" can be configured independently, allowing both global and in-subnet reservations to coexist.

Notice that for global , the client does not need to match a pool.

Configuring databases

When configuring database credentials in the hosts-database or hosts-databases fields in the file configuration, reservations are dynamically searched at allocation time in the databases. The tables that administrators need to populate are hosts , ipv6_reservations , dhcp4_options , and dhcp6_options .

An easy way to populate them consistently is by using the host_cmds hook. Refer to the Kea ARM for instructions.

In a typical network, clients with host reservations are the exception, rather than the rule. However, if host reservations are used, Kea has to check for the existence of a reservation with every client request (see this flow chart in the ARM). This can be a significant performance burden, which is why Kea has options to limit both the number of identifiers evaluated and the scope of the reservation.

For more information on Kea performance optimization, see this related article .

There are a few differences in the handling of host reservations that should be considered when migrating from ISC DHCP to Kea.

Notable differences:

The Kea Migration Assistant ( keama ) can migrate some elements of your existing ISC DHCP configuration to a new Kea configuration. Specifically, the -N option is relevant to host reservation migration, with N being the subnet ID: by default, HRs are migrated as global HRs in a Kea configuration. Running keama -N causes them to be placed in the appropriate subnet.

Example command: keama -6 -i ./dhcp.conf -o ./kea.conf

Corresponding configuration fields from ISC DHCP to Kea DHCP:

Example 1 for ISC DHCP:

Example 1 migrated to Kea:

Example 2 for ISC DHCP:

Example 2 migrated to Kea:

Related articles

• Kea Performance Optimization

What's Next

• Using the Kea Configuration Backend

Table of contents

• host reservations
• static host
• reservation
• static reservations
• kea configuration
• host reservation

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DHCP_IP_RESERVATION_V4 structure (dhcpsapi.h)

The DHCP_IP_RESERVATION_V4 structure defines a client IP reservation. This structure extends an IP reservation by including the type of client (DHCP or BOOTP) holding the reservation.

ReservedIpAddress

DHCP_IP_ADDRESS value that contains the reserved IP address.

ReservedForClient

DHCP_CLIENT_UID structure that contains the hardware address (MAC address) of the DHCPv4 client that holds this reservation.

bAllowedClientTypes

Value that specifies the DHCPv4 reserved client type. The possible values are below:

Requirements

DHCP_IP_ADDRESS

DHCP_IP_RESERVATION_INFO

DHCP_IP_RESERVATION_V6

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