PostgreSQL offers data types to store IPv4, IPv6, and MAC addresses, as shown in Table 8-21. It is better to use these types instead of plain text types to store network addresses, because these types offer input error checking and specialized operators and functions (see Section 9.12).
Table 8-21. Network Address Types
|cidr||7 or 19 bytes||IPv4 and IPv6 networks|
|inet||7 or 19 bytes||IPv4 and IPv6 hosts and networks|
|macaddr||6 bytes||MAC addresses|
When sorting inet or cidr data types, IPv4 addresses will always sort before IPv6 addresses, including IPv4 addresses encapsulated or mapped to IPv6 addresses, such as ::10.2.3.4 or ::ffff:10.4.3.2.
The inet type holds an IPv4 or IPv6 host address, and optionally its subnet, all in one field. The subnet is represented by the number of network address bits present in the host address (the "netmask"). If the netmask is 32 and the address is IPv4, then the value does not indicate a subnet, only a single host. In IPv6, the address length is 128 bits, so 128 bits specify a unique host address. Note that if you want to accept only networks, you should use the cidr type rather than inet.
The input format for this type is address/y where address is an IPv4 or IPv6 address and y is the number of bits in the netmask. If the /y portion is missing, the netmask is 32 for IPv4 and 128 for IPv6, so the value represents just a single host. On display, the /y portion is suppressed if the netmask specifies a single host.
The cidr type holds an IPv4 or IPv6 network specification. Input and output formats follow Classless Internet Domain Routing conventions. The format for specifying networks is address/y where address is the network represented as an IPv4 or IPv6 address, and y is the number of bits in the netmask. If y is omitted, it is calculated using assumptions from the older classful network numbering system, except it will be at least large enough to include all of the octets written in the input. It is an error to specify a network address that has bits set to the right of the specified netmask.
Table 8-22 shows some examples.
Table 8-22. cidr Type Input Examples
|cidr Input||cidr Output|
The essential difference between inet and cidr data types is that inet accepts values with nonzero bits to the right of the netmask, whereas cidr does not.
Tip: If you do not like the output format for inet or cidr values, try the functions
The macaddr type stores MAC addresses, known for example from Ethernet card hardware addresses (although MAC addresses are used for other purposes as well). Input is accepted in the following formats:
These examples would all specify the same address. Upper and lower case is accepted for the digits a through f. Output is always in the first of the forms shown.
IEEE Std 802-2001 specifies the second shown form (with hyphens) as the canonical form for MAC addresses, and specifies the first form (with colons) as the bit-reversed notation, so that 08-00-2b-01-02-03 = 01:00:4D:08:04:0C. This convention is widely ignored nowadays, and it is relevant only for obsolete network protocols (such as Token Ring). PostgreSQL makes no provisions for bit reversal, and all accepted formats use the canonical LSB order.
The remaining four input formats are not part of any standard.