Changing providers is just one possible reason for renumbering.

Part of the motivation for NAT is to avoid the high cost of renumbering inherent in the current IPv4 Internet.

If a site changes its provider, then to avoid injecting additional overhead in the Internet routing system, the site may need to renumber.

Thus if a subscriber changes its provider, then to avoid injecting additional overhead in the Internet routing system, the subscriber may need to renumber.

Localizing address administration to the NAT minimizes renumbering costs, and simultaneously provides for a much larger local pool of addresses than is available under current allocation guidelines.

Summary Due to dynamic address allocation and increasingly frequent network renumbering, temporal uniqueness of IPv4 addresses is no longer globally guaranteed, which puts their use as identifiers into severe question.

Due to dynamic address allocation and increasingly frequent network renumbering, temporal uniqueness of IPv4 addresses is no longer globally guaranteed, which puts their use as identifiers into severe question.