HRA Exemption if rent is more than 1L

Sir , As per notification from CBDT regarding HRA exemption for rent more than 1L PAN no of landlord need to be provided and in absence of it undertaking is required from landlord. My question is what other options if landlord does not provide Pan no? what shiuld me matter in undertaking letter? Any other Way as most of landlord will not provide PAN no.? Please guide us