DHCP Options Sets are configuration sets used in Amazon VPC to configure DHCP (Dynamic Host Configuration Protocol) parameters for virtual machines and other resources within a VPC. These sets allow you to control which parameters will be passed to DHCP clients (e.g., virtual machines) when they join the network and receive IP addresses.

Key Components of DHCP Options Sets

• Domain Name System (DNS) Servers: Specifies one or more DNS servers to be used by resources within the VPC to resolve domain names. These can be either internal or external servers.
• NTP (Network Time Protocol) Servers: Defines one or more NTP servers that resources will use to synchronize time.
• Domain Name: Specifies the domain name that resources will use within the VPC. For example, you can configure an internal domain for your resources to communicate with each other via DNS.
• NetBIOS Servers (optional, for Windows resources): These options are configured to support Windows services that rely on NetBIOS, such as NetBIOS over TCP/IP.
• NetBIOS Node Type: Defines the NetBIOS name resolution method that will be used by clients connected to the network (e.g., B-node, P-node, etc.).

Example Use Case

When virtual machines (e.g., EC2 instances) in a VPC connect to the network and request an IP address, the DHCP server automatically assigns an IP and sends a set of parameters from the DHCP Options Sets. These parameters may include:

• DNS Servers: For configuring VPC resources to use a private DNS server for domain name resolution within the network.
• NTP Servers: For synchronizing time with corporate NTP servers.
• Domain Name: So that all resources in the VPC can use the same domain name.

Why Use DHCP Options Sets?

Configuring DHCP Options Sets provides flexibility in managing network configurations for all resources within the VPC. Instead of manually configuring DNS, time, and domain parameters on each resource, you can use DHCP option sets to centrally manage these settings for all machines connected to your VPC.

Creating a DHCP Options Set

To create a DHCP Options Set:

1. Go to Network > DHCP Options Sets.
2. On the top toolbar, click Create.

In the "Create DHCP Options" dialog, enter the following information on the appropriate tab.

"Details" Tab:

• Name: The name of the DHCP options set.
• Description: An optional description of the DHCP options set.
• DNS Domain: The valid DNS domain name (e.g., xxx.com).

"Servers" Tab:

DNS Servers: The IP address of the DNS server associated with the defined DHCP options set. Defining a DNS server is optional.

NTP Servers: The IP address of the NTP server associated with the defined DHCP options set. Defining an NTP server is optional.

"Netbios" Tab:

Netbios Node Type – The following types can be selected:

• Type 1 – B-node
• Type 2 – P-node
• Type 4 – M-node
• Type 8 – H-node

Click Done.