Why use IPv4 subnet re-purposing?

Manage address depletion

The networking industry is facing the depletion of un-allocated IPv4 address space. To enable service providers to grow in business, techniques have been introduced to use IPv4 address space more efficiently. While dynamic IP allocation mechanisms like DHCP make it easy to assign new IPv4 addresses to endpoints, it is an operational challenge to update static addresses because all endpoints in the corresponding subnet must be updated accordingly.

The major challenge with traditional resource management is that pools are typically used for one purpose only. Providers would have pools of IPv4 addresses, specific for subscriber host addresses, business services, in-band management, control-plane loopback addresses, transfer networks, management systems, gateway addresses, etc. If operators implement a strategy like using /31 instead of /30 for network interfaces, the freed address space can be used for other purposes. However, only complete address blocks can be taken from one pool and added to another pool.

Under the principle of multi-purpose pools, operators do not need to define dedicated pools for single purposes. Especially for public IPv4 addresses, a single IPv4 pool is sufficient. Every address block inside the pool has purpose tags assigned so that the operator can decide the purpose for each address block. If demand changes over time, the purpose tags can be updated. When address blocks can be assigned multiple purpose tags, they can be used more universally. In addition, purpose tags are only used for new allocations: the user can update the address block purpose without affecting existing reservations or allocations. If all purpose tags are removed from an address block, no new reservations are allocated, providing an efficient method to drain an address block.