An engineer is designing an IPv4 addressing plan for an enterprise with 1000 branches. Each branch requires a prefix for data and a prefix for voice. Each prefix must accommodate up to 128 hosts…

Using /24 prefixes from 10.0.0.0/15 and 172.16.0.0/15 means splitting data and voice into completely different private address ranges, which might not be the simplest for identification and would prevent summarization for a branch's data and voice segments into a single, larger prefix.

A /24 prefix can accommodate 254 usable hosts, which meets the "up to 128 hosts" requirement for both data and voice. Using /24 prefixes from the 10.0.0.0/8 private address space and assigning contiguous /24 prefixes for data and voice (e.g., 10.X.Y.0/24 for data, 10.X.Y.255/24 for voice, or 10.X.Y.0/24 for data and 10.X.Z.0/24 for voice where Z immediately follows Y) allows for easy identification of voice prefixes and facilitates summarization at aggregation points. This scheme can easily scale to 1000 branches using the vast 10.0.0.0/8 range.

A /25 prefix only supports 126 usable hosts, which just barely meets "up to 128 hosts," leaving no room for growth and potentially wasting address space if 128 is a hard requirement. Using contiguous /25 prefixes from 10.0.0.0/8 is less efficient for summarization than /24s when you have sufficient space.

Using /24 prefixes from 10.0.0.0/8 and 172.16.0.0/12 again splits data and voice into different private address ranges, hindering summarization at aggregation points and making identification less straightforward than contiguous prefixes within a single range.