ipWhy an address changes
A static IP is provisioned to remain fixed for a connection. A dynamic address can change according to the provider’s assignment process. A dynamic address staying the same for days does not make it static, and restarting a router does not guarantee a new address.
When it matters
A static address can help with a corporate allowlist or certain remote-access setups. Ordinary browsing at home usually does not require one. Do not confuse a local DHCP reservation with a static public IP from an ISP: one concerns your internal network and the other your external connection.
How to observe changes
Check your public IP on different days and record the date and connection type. With a VPN enabled, changes may reflect the VPN exit instead. If an external service is unreachable, ask your provider about CGNAT as well as address changes.
When an allowlist stops working
If a corporate application rejects access today, compare your current public IP with its allowlist entry. If it changed, provide the new address through the approved channel. If it matches, investigate the account, VPN path, and service status. Allowlisting an entire provider range merely because your address changes can grant unnecessary access.
Further reading
DHCP — RFC 2131 ↗Put it into practice
Inspect one public IP, or compare a list of addresses with the bulk lookup tool. Location results are approximate.
Single lookup ↗ Bulk lookup ↗