Matches any valid IPv4 address with, optionally, a CIDR suffix.
0.0.0.0
to 255.255.255.255
and 1.1.1.1/0
to 1.1.1.1/32
.
Use the following regex if you don't want to allow the CIDR suffix.
/^(?:(?:[1-9]?[0-9]|1[0-9][0-9]|2(?:[0-4][0-9]|5[0-5]))\.){3}(?:[1-9]?[0-9]|1[0-9][0-9]|2(?:[0-4][0-9]|5[0-5]))$/
(removed
(?:\/(?:[12]?[0-9]|3[0-2]))?
from the end)