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Subnet
A subnet is a unique CIDR block with a range of IP addresses in a VPC. All resources in a VPC must be deployed on subnets.
By default, all instances in different subnets of the same VPC can communicate with each other and the subnets can be located in different AZs. If you have a VPC with two subnets in it and they are located in different AZs, they can communicate with each other by default.
After a subnet is created, its CIDR block cannot be modified. Subnets in the same VPC cannot overlap.
A subnet mask can be between the netmask of its VPC CIDR block and /29 netmask. If a VPC CIDR block is 10.0.0.0/16, its subnet mask can between 16 to 29.
For example, if the CIDR block of VPC-A is 10.0.0.0/16, you can specify 10.0.0.0/24 for subnet A01, 10.0.1.0/24 for subnet A02, and 10.0.3.0/24 for subnet A03.
Note
By default, you can create a maximum of 100 subnets in each region. If this cannot meet your service requirements, request a quota increase by referring to
What Is a Quota? <vpc_faq_0051>