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. You can use DHCP options sets to configure DNS server IP addresses and domain names 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 lists the regions that support DHCP options sets.
Area Supported region
Asia Pacific China (Beijing), China (Zhangjiakou), China (Hangzhou), China (Shanghai), China (Shenzhen), China (Chengdu), China (Hong Kong), Japan (Tokyo), Singapore (Singapore), Australia (Sydney), Malaysia (Kuala Lumpur), and Indonesia (Jakarta)
Europe & Americas US (Virginia), US (Silicon Valley), Germany (Frankfurt), and UK (London)
Middle East & India India (Mumbai) and UAE (Dubai)

Features

By default, the IP addresses of the Alibaba Cloud DNS servers are specified for the ECS instance that you create. The 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 VPC 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 lists the domain names and DNS server IP addresses in DHCP options sets.
DHCP option Description
Domain name The root domain of the ECS instance, such as example.com.
DNS server IP address The IP addresses of the DNS servers.
The IP addresses of the 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 on Alibaba Cloud. You can also specify up to four custom DNS server IP addresses to meet your business requirements.
Notice Before you specify custom DNS server IP addresses, take note of the following limits:
  • The system automatically specifies the IP addresses of the 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 to only the security group. For more information, see Add security group rules and Add rules to a 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 to trigger the synchronization. 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 in a VPC that has VPC sharing enabled. For more information, see Overview.

Limits

Before you use DHCP options sets, we recommend that you understand the following limits.
Item Default limit Quota increase
Number of DHCP options sets that can be created with each Alibaba Cloud account 10 N/A
Number of VPCs that can be associated with each DHCP options set 10
Number of DHCP options sets that can be associated with each VPC 1
Number of domain names that can be specified in each DHCP options set 1
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 VPCs that contain ECS instances of the following instance families:

ecs.c1, ecs.c2, ecs.c4, 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.

Upgrade or release an Elastic Compute Service (ECS) instance that does not support advanced network features.

Work with DHCP options sets

For more information, see Work with DHCP options sets.