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 synchronize predefined DNS server IP addresses and domain names to Elastic Compute Services (ECS) instances in virtual private clouds (VPCs).

Note The DHCP options sets feature is in public preview and is available only in the following regions: China (Chengdu), India (Mumbai), Malaysia (Kuala Lumpur), Indonesia (Jakarta), UAE (Dubai), and UK (London). To use the DHCP options sets feature in the preceding regions,submit a ticket.
DHCP options sets

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.

To resolve this problem, you can create DHCP options sets and associate DHCP options sets with VPCs. After a DHCP options set is associated with a VPC, existing and new ECS instances in the VPC all use the configurations of the associated DHCP options set. For more information, see How DHCP options sets are applied.

The following table lists the DHCP options supported by a DHCP options set.
DHCP option Description
Domains The root domain of the ECS instances, for example, example.com.
DNS server IP address The IP addresses of 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, note 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 on Alibaba Cloud. Proceed with caution.
  • You must add rules to the security group and network ACL (if any) to enable access to the specified custom DNS servers. Otherwise, the services deployed on your ECS instances cannot be resolved. For more information, see Add security group rules and Add network ACL rules.

How DHCP options sets are applied

The following table describes how a DHCP options set is applied to new and existing ECS instances 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 ECS instances
  • Restart the DHCP Client service
  • Restart the network connection 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 created in a VPC that has VPC sharing enabled. For more information, see Shared VPC overview.

Limits

Before you use DHCP options sets, you must understand the following limits.
Service Default Quota increase
Maximum number of DHCP options sets that can be created for a VPC 10 N/A
Maximum number of DHCP options sets that can be associated with a VPC 1 N/A
Maximum number of VPCs that can be associated with a DHCP options set 10 N/A
Maximum number of domain names that can be specified in a DHCP options set 1 N/A
Maximum number of DNS server IP addresses that can be specified in a DHCP options set 4 N/A
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.

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.