Contents
Introduction
A DHCP Fixed Address makes a particular IP address available for use exclusively by a single designated client. For as long as the Fixed Address is configured, the designated client will always receive this IP address when connected to the appropriate network, and this IP address will never be allocated to any other client. For DHCPv4, the designated client is identified by MAC address; for DHCPv6, it is identified by DUID (DHCP Unique Identifier – see also Limitations of DHCPv6 fixed address allocation).
From the client’s point of view, obtaining a lease from a Fixed Address is exactly the same as obtaining a lease from a DHCP Range.
On the server side, however, there is an important difference: fixed addresses are timeless, which is to say that the server’s behavior does not take into account whether the IP address in question was previously leased (either to the same client or to a different client). This has two practical consequences for the careful network administrator wishing to avoid an operational conflict:
- Avoid configuring a Fixed Address for an IP which currently has an Active lease belonging to a different client (unless you are certain that the old client is no longer on the network).
- Avoid configuring a Fixed Address for an IP which very recently had a Fixed Address belonging to a different client (unless you are certain that the old client is no longer on the network).
Stand-alone Fixed Addresses vs DHCP-enabled Host records
The stand-alone DHCP Fixed Address objects described on the remainder of this page are DHCP-only objects with no DNS component.
You may alternatively wish to consider enabling DHCP for an IP address within a Host record, which is functionally equivalent to creating a stand-alone Fixed Address but makes it easy to keep the DNS and DHCP configuration for a client in sync (in case you later decide to migrate the client to a different IP address or retire it altogether).
Best practice: in general, use DHCP-enabled Host records instead of stand-alone DHCP Fixed Addresses.
Reservations
You may notice that it’s also possible in IPAM to create a “Reservation” object. This is not the same thing as a Fixed Address, and will not accomplish what you probably intend; a “Reservation” in IPAM is a placeholder which does not permit any DHCP client to use the IP.
Users familiar with Microsoft DHCP should note that a Microsoft DHCP “Reservation” is analogous to a Fixed Address in IPAM, not a “Reservation”.
Creating a DHCP Fixed Address
To create a new stand-alone DHCP Fixed Address:
- Using either DHCP View or IPAM View, Open the Network in which you want to add a fixed address (see Getting Started with IPAM).
- Optionally (if using IPAM View), select the checkbox next to the desired IP address.
- Click the dropdown arrow next to the Add (+) icon above the table in the main workspace, then choose “Fixed Address”.
- Click “Next” at the bottom of the dialog window.
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Enter the desired IP address.
If you have opened a Network in IPAM View and selected an IP address in the main workspace, it will automatically be pre-populated for you.
- For IPv4 addresses: ensure that “MAC Address” is selected, and enter the MAC address of the client that will use this IP.
- For IPv6 addresses: enter the DUID (DHCP Unique Identifier – see also Limitations of DHCPv6 fixed address allocation) of the client that will use this IP.
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Optionally, you may use the Name field to specify an internal display name for this Fixed Address object.
The Name field does not create a DNS hostname! If you want to manage DNS and DHCP for this client together, consider adding DHCP to a Host record instead of creating a stand-alone Fixed Address.
- Click “Save & Close”.
Please note that your network must have autoconfiguration service appropriately enabled (see Requesting DHCP for Networks) in order for creating a DHCP Fixed Address to have any effect.
Editing a Fixed Address
To edit an existing stand-alone DHCP Fixed Address:
- Navigate to the Fixed Address you want to edit (e.g. by opening its Network in DHCP View, or opening the individual IP address in IPAM View to display Related Objects – see Getting Started with IPAM).
- Select the checkbox for the Fixed Address object, and click the Edit (notepad) icon above the table.
- Make sure to enable Advanced Mode for the dialog.
- Make any desired changes.
- Click “Save & Close”.
Note that you can configure custom DHCP options that will apply only to this individual fixed address (but are otherwise similar to Setting DHCP Options for a Range).
Deleting a Fixed Address
To deleted an existing stand-alone DHCP Fixed Address:
- Navigate to the Fixed Address you want to edit (e.g. by opening its Network in DHCP View, or opening the individual IP address in IPAM View to display Related Objects – see Getting Started with IPAM).
- Select the checkbox for the Fixed Address object (making sure no other checkboxes are selected), and click the Delete (trash can) icon above the table.
- If you’re sure, click “Yes” when the confirmation dialog appears.