This topic describes FAQ about CIDR blocks.

What is CIDR?

Classless Inter-Domain Routing (CIDR) is a new addressing method on the Internet. Compared with traditional Class A, B, or C addressing, CIDR allocates IP addresses more efficiently. For example, the IP addresses ranging from 125.203.96.0 to 125.203.127.255 can be coverted into the following CIDR format:

125.203.0110 0000.0000 0000 to 125.203.0111 1111.1111 1111, or 125.203.96.0/19.

When you create a VPC or a VSwitch, you must specify its IP address range in the form of a CIDR block.

How do I specify the CIDR block of a VPC?

You can specify the CIDR block of a VPC to 192.168.0.0/16, 172.16.0.0/12, 10.0.0.0/8, and their subnets. The valid netmask range is between /8 and /24.

For more information, see Create a VPC.

How do I specify the CIDR block of a VSwitch?

When you specify the CIDR block of a VSwitch, the following rules apply:
  • The CIDR block of the VSwitch must belong to the CIDR block of the corresponding VPC. If the CIDR block of the VSwitch is identical to that of the VPC, you can only create one VSwitch.
  • The netmask range of the VSwitch is between /16 and /29.
  • The CIDR block of the VSwitch cannot be identical to the CIDR blocks of any existing VSwitch.
  • The CIDR block of the VSwitch cannot be identical to the destination CIDR block of any route entry in the VPC.
  • The CIDR block of the VSwitch cannot contain the destination CIDR block of any route entry in the VPC, but can be the subnet of the destination CIDR block.

For more information, see Create a VSwitch.