IP address allocation

Hi,

I've googled but haven't really come across anything that answers my questions. Is it common practice for ISPs to allocate a block of addresses to a customer and put in DNS records for ones that are unused?

For example, xxx.8-xxx.15 is assigned to the customer. Customer uses xxx.9 for the router and xxx.10 for web server. xxx.11-14 are unused. I would expect to see DNS records for xxx.9 and xxx.10 but not for the rest of the block. Am I wrong? If there are DNS records for the rest of the IPs, why is that? Is there some security reason for doing this?

-- 
Regards,
Terry


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