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).
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.
|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:
How DHCP options sets are applied
|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.
|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.|
|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.