I am looking for an access control solution utilizing either software
(proxy) or hardware (gateway/router) to monitor and authorize use of a
workstations TCP/IP resources.

Proposed flow:
1. Client (IP: 123.456.789.001) connects to Host (IP: 789.456.123.001)
on generic port 99.
2. Host machine verifies incoming IP address against simple and
dynamically updatable DB.
3. If client IP is validated against the DB: Host passes connection
off to 789.456.123.002:99. Otherwise, connection is dropped.

Requirements:
- IP verification only. No fancy software or tunneling allowed on client's machine.
- Athorization information must be updatable without reloading service.
- Established connection can be terminated by the initial host machine
with access to the authorization data.
- Workstation should not require any configuration changes.