What is the most appropriate data type for storing an IP address in SQL server?

Regarding this comment in the accepted answer

sorting them is a pain unless you pad zeros.

Here's a trick for SQL Server 2008 (From Itzik Ben-Gan in this book)

with ip_addresses as
(
SELECT '131.33.2.201' AS ip_address UNION ALL
SELECT '2.12.4.4' AS ip_address UNION ALL
SELECT '131.33.2.202' AS ip_address UNION ALL
SELECT '2.12.4.169' AS ip_address UNION ALL
SELECT '131.107.2.201' AS ip_address 
)
select ip_address
from ip_addresses
ORDER  BY CAST('/' + ip_address + '/' AS hierarchyid)

Returns

ip_address
-------------
2.12.4.4
2.12.4.169
131.33.2.201
131.33.2.202
131.107.2.201

For space efficient storage and when the values are to be processed (matched or compared to a range), I use an int. The IP address really is just a 32 bit value.

For a simple solution where you just want to store the value to view it, I use a varchar(15) to store the string representation of the IP adress.

Storing an IPv4 address as a binary(4) is truest to what it represents, and allows for easy subnet mask-style querying. However, it requires conversion in and out if you are actually after a text representation. In that case, you may prefer a string format.

A little-used SQL Server function that might help if you are storing as a string is PARSENAME, by the way. Not designed for IP addresses but perfectly suited to them. The call below will return '14':

SELECT PARSENAME('123.234.23.14', 1)

(numbering is right to left).

I normally just use varchar(15) for IPv4 addresses - but sorting them is a pain unless you pad zeros.

I've also stored them as an INT in the past. System.Net.IPAddress has a GetAddressBytes method that will return the IP address as an array of the 4 bytes that represent the IP address. You can use the following C# code to convert an IPAddress to an int...

var ipAsInt = BitConverter.ToInt32(ip.GetAddressBytes(), 0);

I had used that because I had to do a lot of searching for dupe addresses, and wanted the indexes to be as small & quick as possible. Then to pull the address back out of the int and into an IPAddress object in .net, use the GetBytes method on BitConverter to get the int as a byte array. Pass that byte array to the constructor for IPAddress that takes a byte array, and you end back up with the IPAddress that you started with.

var myIp = new IPAddress(BitConverter.GetBytes(ipAsInt));