Dynamic Host Configuration Protocol (DHCP) is a network management protocol. DHCP provides a standard for passing configuration information to servers in a TCP/IP network. The DHCP options sets feature allows you to configure domain names and DNS server IP addresses for Elastic Compute Service (ECS) instances that are deployed in a virtual private cloud (VPC).

DHCP options sets

Feature release and supported regions

The following table describes the regions that support DHCP options sets.
Area Region
Asia Pacific

China (Beijing), China (Zhangjiakou), China (Hohhot), China (Hangzhou), China (Shanghai), China (Shenzhen), China (Guangzhou), China (Chengdu), China (Hong Kong), Japan (Tokyo), South Korea (Seoul), Singapore, Australia (Sydney), Malaysia (Kuala Lumpur), Indonesia (Jakarta), Philippines (Manila), Thailand (Bangkok), and India (Mumbai)
Europe and Americas Germany (Frankfurt), UK (London), US (Silicon Valley), and US (Virginia)
Middle East UAE (Dubai)

Features

By default, the IP addresses of Alibaba Cloud DNS servers are specified for the ECS instance that you create. Alibaba Cloud DNS servers cannot resolve private domain names. You can specify custom DNS server IP addresses for your ECS instance. However, the custom configurations are cleared after you restart the ECS instance.

VPCs support DHCP options sets. You can specify domain names and DNS server IP addresses for a DHCP options set. Then, you can associate the DHCP options set with one or more VPCs that belong to the same region. Then, newly created ECS instances in the VPCs use the configurations of the DHCP options set. After the DHCP options set is synchronized to existing ECS instances, existing ECS instances also use the configurations of the DHCP options set. For more information, see How DHCP options sets are applied to ECS instances.

The following table describes the domain names and DNS server IP addresses in DHCP options sets.
DHCP option Description
Domain name The root domain of the ECS instance, for example, example.com.
DNS server IP address The IP addresses of the DNS servers.
The IP addresses of Alibaba Cloud DNS servers, which are 100.100.2.136 and 100.100.2.138, are used by default. This ensures that you can access basic services deployed on Alibaba Cloud. You can also specify at most four custom DNS server IP addresses to meet your business requirements.
Important Before you specify custom DNS server IP addresses, take note of the following limits:
  • The system automatically specifies the IP addresses of Alibaba Cloud DNS servers, which are 100.100.2.136 and 100.100.2.138. If you delete these IP addresses, you may not be able to access the basic services deployed on Alibaba Cloud. Proceed with caution.
  • You must add rules to the security group and network access control lists (ACLs) to enable access to the specified custom DNS servers. Otherwise, the services deployed on your ECS instances cannot be resolved. If network ACLs do not exist, add rules only to the security group. For more information, see Add a security group rule and Add rules to the network ACL.

How DHCP options sets are applied to ECS instances

The following table describes how a DHCP options set is applied to new and existing ECS instances deployed in a VPC after the DHCP options set is associated with the VPC.
Instance type Rule
Existing ECS instances (ECS instances that are created in the VPC before the DHCP options set is associated with the VPC). If one of the following operations is performed, the DHCP options are synchronized to the existing ECS instances in the VPC:
  • Restart the ECS instance.
  • Restart the DHCP Client service.
  • Restart the network service.
New ECS instances (ECS instances that are created in the VPC after the DHCP options set is associated with the VPC). No operation is required. The DHCP options are automatically synchronized to the newly created ECS instances in the VPC.
Note DHCP options sets are also applicable to ECS instances that are created in a VPC for which VPC sharing is enabled. For more information, see Overview of VPC sharing.

Limits

Item Limit Adjustable
Maximum number of DHCP options sets that can be created with each Alibaba Cloud account 10 No.
Maximum number of VPCs that can be associated with each DHCP options set 10
Maximum number of DHCP options sets that can be associated with each VPC 1
Maximum number of domain names that can be specified in each DHCP options set 1
Maximum number of DNS server IP addresses that can be specified in each DHCP options set 4
VPCs that cannot be associated with DHCP options sets If a VPC contains an ECS instance that belongs to one of the following instance families, the VPC does not support DHCP options sets:

ecs.c1, ecs.c2, ecs.c4, ecs.c5, ecs.ce4, ecs.cm4, ecs.d1, ecs.e3, ecs.e4, ecs.ga1, ecs.gn4, ecs.gn5, ecs.i1, ecs.m1, ecs.m2, ecs.mn4, ecs.n1, ecs.n2, ecs.n4, ecs.s1, ecs.s2, ecs.s3, ecs.se1, ecs.sn1, ecs.sn2, ecs.t1, and ecs.xn4.

For more information, see Advanced VPC features.

If your Elastic Compute Service (ECS) instance does not support advanced virtual private cloud (VPC) features, upgrade or release the ECS instance.

Use DHCP options sets

For more information, see Work with DHCP options sets.