["192.168.2.0",
 "192.168.2.1",
 "192.168.2.2",
 "192.168.2.3",
 "192.168.2.4",
 "192.168.2.5"]

ip = '192.168.2.0'

ips = 0.upto(5).map do |n|
  ip.sub(/.d+$/, '.' << n.to_s)
end

require 'ipaddr'
ip = "192.168.2.0"

ips = [ip]
5.times do
  ips << IPAddr.new(ips.last).succ.to_s
end
p ips
# =>["192.168.2.0", "192.168.2.1", "192.168.2.2", "192.168.2.3", "192.168.2.4", "192.168.2.5"]

#Ranges work:
ip_range = IPAddr.new("192.168.2.0")..IPAddr.new("192.168.2.5")
p ip_range.map(&:to_s)
# =>["192.168.2.0", "192.168.2.1", "192.168.2.2", "192.168.2.3", "192.168.2.4", "192.168.2.5"]

ip = '192.168.2.0'

p (0...5).inject([ip]) { |l| l << l.last.succ }

#=> ["192.168.2.0", "192.168.2.1", "192.168.2.2", "192.168.2.3", "192.168.2.4", "192.168.2.5"]

p (0..255).inject([ip]) { |l, d| l << (l.last.split('.')[0..2] << d).join('.') }

#=> ["192.168.2.0" ... "192.168.2.255"]

require 'ipaddr'
current = ip = IPAddr.new('192.168.2.0')
array = [ip]
until current.to_s == '192.168.2.5'
  array << current = current.succ
end
array.map!(&:to_s)

ip = '192.168.2.0'

ips = 0.upto(5).map do |n|
  ip.split('.').tap{|i| i[-1] = n }.join('.')
end