Oracle Cloud Infrastructure Documentation

DHCP Options

This topic describes how to manage the Dynamic Host Configuration Protocol (DHCP) options in a virtual cloud network (VCN).

Warning

Avoid entering confidential information when assigning descriptions, tags, or friendly names to your cloud resources through the Oracle Cloud Infrastructure Console, API, or CLI.

Overview of DHCP Options

The Networking service uses DHCP to automatically provide configuration information to instances when they boot up. Although DHCP lets you change some settings dynamically, others are static and never change. For example, when you launch an instance, either you or Oracle specifies the instance's private IP address. Each time the instance boots up or you restart the instance's DHCP client, DHCP passes that same private IP address to the instance. The address never changes during the instance's lifetime.

The Networking service provides DHCP options to let you control certain types of configuration on the instances in your VCN. You can change the values of these options at your discretion, unlike the static information that DHCP provides to the instance. The changes take effect the next time you restart a given instance's DHCP client or reboot the instance. For more details, see Important Notes about Your Instances and DHCP Options.

Each subnet in a VCN can have a single set of DHCP options associated with it. That set of options applies to all instances in the subnet. Each VCN comes with a default set of DHCP options with initial values that you can change. If you don't specify otherwise, every subnet uses the VCN's default set of DHCP options.

The following table summarizes the available DHCP options you can configure.

DHCP Option Possible Values Initial Value in the Default DHCP Options Notes
Domain Name Server

DNS Type:

  • Internet and VCN Resolver
  • Custom Resolver
DNS Type = Internet and VCN resolver. For more information, see Choices for DNS in Your VCN. If you set DNS Type = Custom Resolver, you can specify up to three DNS servers of your choice. For more information, see Choices for DNS in Your VCN.
Search Domain A single search domain

If you've set up your VCN with a DNS label, the default value for the Search Domain option is the VCN domain name (<VCN DNS label>.oraclevcn.com). Otherwise, the Search Domain option is not present in the default set of DHCP options.

In general, when any set of DHCP options is initially created (the default set or a custom set you create), the Networking service automatically adds the Search Domain option and sets it to the VCN domain name (<VCN DNS label>.oraclevcn.com) if all of these are true:

  • The VCN has a DNS label
  • DNS Type = Internet and VCN Resolver
  • You did NOT specify a search domain of your choice during creation of the set of DHCP options

After the set of DHCP options is created, you can always remove the Search Domain option or set it to a different value.

You can specify only a single search domain in a set of DHCP options.

Working with DHCP Options

When you create a subnet, you specify which set of DHCP options to associate with the subnet. If you don't, the default set of DHCP options for the VCN is used. You can change which set of DHCP options the subnet uses at any time.

When creating a new set of DHCP options, you may optionally assign it a friendly name. It doesn't have to be unique, and you can change it later. Oracle automatically assigns the set of options a unique identifier called an Oracle Cloud ID (OCID). For more information, see Resource Identifiers.

You can change the values of an individual DHCP option in a set, but notice that when you use the REST API to update a single option in a set, the new set of options replaces the entire existing set.

To delete a set of DHCP options, it must not be associated with a subnet yet. You can't delete a VCN's default set of DHCP options.

For information about the maximum number of DHCP options allowed, see Service Limits.

Required IAM Policy

To use Oracle Cloud Infrastructure, you must be given the required type of access in a An IAM document that specifies who has what type of access to your resources. It is used in different ways: to mean an individual statement written in the policy language; to mean a collection of statements in a single, named "policy" document (which has an Oracle Cloud ID (OCID) assigned to it); and to mean the overall body of policies your organization uses to control access to resources. written by an administrator, whether you're using the Console or the REST API with an SDK, CLI, or other tool. If you try to perform an action and get a message that you don’t have permission or are unauthorized, confirm with your administrator the type of access you've been granted and which A collection of related resources that can be accessed only by certain groups that have been given permission by an administrator in your organization. you should work in.

For administrators: see IAM Policies for Networking.

Important Notes about Your Instances and DHCP Options

Whenever you change the value of one of the DHCP options, you must do one of the following for the change to take effect on existing instances in the subnets associated with that set of DHCP options: either restart the DHCP client on the instance, or reboot the instance.

Make sure to keep the DHCP client running so you can always access the instance. If you stop the DHCP client manually or disable NetworkManager (which stops the DHCP client on Linux instances), the instance can't renew its DHCP lease and will become inaccessible when the lease expires (typically within 24 hours). Do not disable NetworkManager unless you use another method to ensure renewal of the lease.

Stopping the DHCP client might remove the host route table when the lease expires. Also, loss of network connectivity to your iSCSI connections might result in loss of the boot drive.

Any changes you make to the /etc/hosts and /etc/resolv.conf files will be overwritten whenever the DHCP lease is renewed or the instance is rebooted. To persist your changes, add the following line to /etc/oci-hostname.conf:

PRESERVE_HOSTINFO=2

If the /etc/oci-hostname.conf file does not exist, create it.

Using the Console

To view a VCN's set of default DHCP options
To update options in an existing set of DHCP options
To create a new set of DHCP options
To change which set of DHCP options a subnet uses
To delete a set of DHCP options
To manage tags for a set of DHCP options

Using the API

For information about using the API and signing requests, see REST APIs and Security Credentials. For information about SDKs, see Software Development Kits and Command Line Interface.

To manage a VCN's DHCP options, use these operations: