A prefix list is a set of one or more network prefixes (CIDR blocks). You can reference prefix lists to configure network rules for other resources. You can add CIDR blocks that are frequently used to prefix lists to avoid repeatedly adding multiple rules for CIDR blocks when you configure network rules and improve O&M efficiency. Prefix lists can be referenced when you configure security group rules.
|Maximum number of entries||The maximum number of CIDR blocks in a prefix list. Each entry consists of a CIDR block and a description for the CIDR block.|
|Address family||The address family of entries in prefix lists. Prefix lists support the IPv4 or IPv6 address type. Entries in a single prefix list must belong to the same address family.|
CIDR is an addressing scheme for the Internet that allows for IP addresses to be assigned in a more efficient manner than the traditional scheme based on classes A, B, and C. CIDR notation is used to denote IP addresses and IP ranges. It consists of an IP address and a forward slash followed by a decimal number that denotes how many bits are in the network prefix.
|Associated resource||Other resources that reference prefix lists.|
|Prefix lists per region within an account||100||N/A|
|Entries in a single prefix list||200||N/A|
|Associated resources of a prefix list||1,000||N/A|
You can maintain CIDR blocks in prefix lists and reference prefix lists in the rules of other resources. When you modify the entry information in a prefix list, the modifications take effect on all rules that reference the prefix list. This eliminates the need to modify multiple entries and improves O&M efficiency.
For example, when you add a rule to a security group, you can reference a prefix list to apply the rule to all CIDR blocks in the prefix list.