attempts to find an interface that'll serve the IP address

find_by_ip_interface.rb

# find_ip_by_interface.rb
#
# Attempts to discover which interface will serve a particular destination
#

require 'ipaddr'

module Puppet::Parser::Functions
    newfunction(:find_ip_by_interface, :type => :rvalue) do |args|
        address = IPAddr.new(args[0])

        retcon = ""

        lookupvar('interfaces').split(',').each do |interface|
            netmask = lookupvar("netmask_#{interface}")
            int_addr = lookupvar("ipaddress_#{interface}")

            int = IPAddr.new("#{int_addr}/#{netmask}")

            if int.include?(address)
                retcon = interface
            end
        end

        retcon
    end
end