As we all know ipv4 exhaustion is a real thing. Our company has already acquired a /24 subnet from ARIN. We are now opening a new datacenter to distribute load across a regional area. The fight with ARIN has suggested that they may not assign us additional IP space since we aren't using our current block fully. We could easily split our /24 into 2 x /25, but none of our ISP's will allow us to advertise anything less than /24.
How do other companies do this? It seems to me that on the ISP side(s), I advertise my /24. And then amongst all the edge routers I could do some iBGP but advertise just the local part of the subnet for that site (a /25). Like the image.