Postgres offers data types to store IP and MAC addresses. It is preferable to use these types over plain text types, because these types offer input error checking and several specialized operators and functions.
Table 3-17. Network Address Data Types
|cidr||12 bytes||IP networks||valid IPv4 networks|
|inet||12 bytes||IP hosts and networks||valid IPv4 hosts or networks|
|macaddr||6 bytes||MAC addresses||customary formats|
IP v6 is not supported, yet.
The inet type holds an IP host address, and optionally the identity of the subnet it is in, all in one field. The subnet identity is represented by the number of bits in the network part of the address (the "netmask"). If the netmask is 32, then the value does not indicate a subnet, only a single host. Note that if you want to accept networks only, you should use the cidr type rather than inet.
The input format for this type is x.x.x.x/y where x.x.x.x is an IP address and y is the number of bits in the netmask. If the /y part is left off, then the netmask is 32, and the value represents just a single host. On display, the /y portion is suppressed if the netmask is 32.
The cidr type holds an IP network specification. Input and output formats follow Classless Internet Domain Routing conventions. The format for specifying classless networks is x.x.x.x/y where x.x.x.x is the network and y is the number of bits in the netmask. If y is omitted, it is calculated using assumptions from the older classful numbering system, except that it will be at least large enough to include all of the octets written in the input.
Here are some examples:
Table 3-18. cidr Type Input Examples
|CIDR Input||CIDR Displayed||abbrev(CIDR)|
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 host(), text(), and abbrev() functions.
The macaddr type stores MAC addresses, i.e., Ethernet card hardware addresses (although MAC addresses are used for other purposes as well). Input is accepted in various customary formats, including '08002b:010203', '08002b-010203', '0800.2b01.0203', '08-00-2b-01-02-03', and '08:00:2b:01:02:03', which would all specify the same address. Upper and lower case is accepted for the digits a through f. Output is always in the latter of the given forms.
The directory contrib/mac in the Postgres source distribution contains tools that can be used to map MAC addresses to hardware manufacturer names.
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