DHCP option sets in Amazon VPC
Network devices in your VPC use Dynamic Host Configuration Protocol (DHCP). You can use DHCP option sets to control the following aspects of the network configuration in your virtual network:
The DNS servers, domain names, or Network Time Protocol (NTP) servers used by the devices in your VPC.
Whether DNS resolution is enabled in your VPC.
What is DHCP?
Every device on a TCP/IP network requires an IP address to communicate over the network. In the past, IP addresses had to be assigned to each device in your network manually. Today, IP addresses are assigned dynamically by DHCP servers using the Dynamic Host Configuration Protocol (DHCP).
Applications running on EC2 instances can communicate with Amazon DHCP servers as needed to retrieve their IP address lease or other network configuration information (such as the IP address of an Amazon DNS server or the IP address of the router in your VPC).
You can specify the network configurations that are provided by Amazon DHCP servers by using DHCP option sets.
If you have a VPC configuration that requires your applications to make direct requests to the Amazon IPv6 DHCP server, note the following:
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An EC2 instance in a dual-stack subnet can only retrieve its IPv6 address from the IPv6 DHCP server. It cannot retrieve any additional network configurations from the IPv6 DHCP server, such as DNS server names or domain names.
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An EC2 instance in a IPv6-only subnet can retrieve its IPv6 address from the IPv6 DHCP server and can retrieve additional networking configuration information, such as DNS server names and domain names.
For an EC2 instance in an IPv6-only subnet, the IPv4 DHCP Server will return 169.254.169.253 as the name server if "AmazonProvidedDNS" is explicitly mentioned in the DHCP option set. If "AmazonProvidedDNS" is missing from the option set, the IPv4 DHCP Server won't return an address whether other IPv4 name servers are mentioned in the option set or not.
The Amazon DHCP servers can also provide an entire IPv4 or IPv6 prefix to a network interface in your VPC using prefix delegation (see Assigning prefixes to Amazon EC2 network interfaces in the Amazon EC2 User Guide). IPv4 prefix delegation is not provided in DHCP responses. IPv4 prefixes assigned to the interface can be retrieved using IMDS (see Instance metadata categories in the Amazon EC2 User Guide).
