can anyone explain me is there a restriction in policy for assigning /48 PI IPv6 to ISP which will use /64-/128 prefixes to connect broadband customers?
Minimum IPv6 allocation to ISPs is /32 which will allow you to assign /48 prefixes to broadband customers. This makes network design simple and you would be following the same mainstream IPv6 implementation rules as most other ISPs. This will make it much easier for you to get support from your vendors and advice from other ISPs who are deploying IPv6. It also prevents your competitors from telling your customers that your service is bad because you give customers a smaller block of addresses/subnets. Really, only mobile phones or other devices should get /128 prefixes. Anything that is a network with potentially two or more devices on it should get a /64. And a broadband customer is a "site" so they should get a whole /48 unless you are very big. Some very big ISPs are giving /56 to customers in their private homes and only give /48 to an office or some kind of business. --Michael Dillon