US 5802320

Patent Overview: US 5,802,320 A

Title: "System for packet filtering of data packets at a computer network interface"

Assignee: Sun Microsystems, Inc. (original assignee; listed current assignee is also Sun Microsystems Inc).

Key dates (per supplied text): Priority/filing date 1995-05-18; published/granted 1998-09-01; anticipated expiration 2015-09-01; status "Expired – Lifetime."

Application number: US08/444,351. Inventors: Baehr, Danielson, Lyon, Mulligan, Patterson, Scott, and Turbyfill. Related later filings cited in the text include US08/795,374 (US5878231A) and US08/795,373 (US5884025A), plus EP, SG, and JP counterparts.

Purpose: The invention screens data packets sent from one computer network to another, addressing the vulnerability of private networks to intruders and to "targeting" (characterization and attack) of filtering systems. Conventional filtering systems act as routers, respond to IP commands, and expose IP addresses. The invention instead provides a "screening system that acts as both a firewall in the conventional sense and a signatureless packet filtering system."

Plain-language scope: A screen sits in-line between, e.g., a public and a private network. It has a network interface for each network plus one or more ports to a proxy network. A packet-filtering module inspects each incoming packet and passes it to an engine, which decides actions based on the inspection and other information; an actions module executes them. If a packet is destined for a private-network host, it may be sent instead to a preconfigured host on the proxy network, which performs the expected (or different) operations. The proxy host generates responses using the actual host's IP address, so the proxy network is undetectable. The screening system is not a router, has no IP address of its own, and is therefore not subject to trace-route, ping, or finger. It requires no changes to the private/public networks and can be configured for other actions (dropping with/without error, logging, header alteration) while preserving anonymity.

Source: https://patents.google.com/patent/US5802320/en

Not established by the excerpt: The full claims and their exact wording; detailed hardware (e.g., FIG. 8), flowcharts (FIGS. 10–11), and embodiment specifics, most of which are omitted. No litigation, ownership-transfer, validity, or prior-art analysis is provided or attempted.