OpenNebula

IPv6 addresses contain ":" character and this is used by OCA library to tell appart IP's and MAC addresses. From virtual_network.rb:

        # Holds a virtual network address
        # @param ip [String] address to hold, if contains ":" a MAC address is assumed
        # @param ar_id [Integer] The address range to hold the lease. If not set
        #        the lease will be held from all possible address ranges
        def hold(ip, ar_id=-1)
            return Error.new('ID not defined') if !@pe_id

            if ip.include?':'
                addr_name = "MAC" 
            else
                addr_name = "IP" 
            end

            lease_template =  "LEASES = [ #{addr_name} = #{ip}" 
            lease_template << ", AR_ID = #{ar_id}" if ar_id != -1
            lease_template << "]" 

            rc = @client.call(VN_METHODS[:hold], @pe_id, lease_template)
            rc = nil if !OpenNebula.is_error?(rc)

            return rc
        end