Key takeaway
Give each exception an owner, purpose, scope and expiry date, then review the list regularly.
Allowlist and denylist
An allowlist permits only listed entities; a denylist blocks known entities while allowing the rest. An allowlist is more restrictive by default, but incorrect or stale entries can block legitimate access. Check the system’s actual default behavior rather than relying on terminology alone.
IP allowlisting within access controls
IP allowlisting is an access-policy mechanism that can be implemented in a firewall or service, rather than an alternative product. Source addresses may be combined with service, port and other supported conditions. Addresses change and may be shared behind NAT or proxies; broad subnets may admit unexpected users. An approved address does not replace identity or authentication or prove benign content.
Review and govern entries
For application and file allowlisting, also define how new software is approved. Govern the lifecycle of access entries in the following sequence.
Request
Record the business reason, required resource and scope.
Verify source and service
Confirm actual egress and service with the owner; avoid broad permission.
Approve narrowly
Grant narrow permission with an owner, approver, expiry and audit record.
Review and revoke
Review changed addresses; expire or revoke stale and unnecessary permission.
Check whether an IP address is allowed
With the system owner’s authorization, inspect the active rule and logs in the firewall or service console. A user’s public egress IP may differ from the device’s local address because of NAT or a proxy; confirm the expected source with the network owner. If access is missing, submit a change request instead of adding an address yourself.