US 5878231

I'll search for this specific patent number across USPTO and CAFC docket sources.

Let me run a few more targeted searches to confirm the litigation/docket status.

Analyst Summary — US Patent 5,878,231

Scope note: I searched for this exact number across patent, PTAB/TTAB, district-court and Federal Circuit materials. The primary source used is the full patent text from Google Patents (fetched 2026‑09‑23). I did not find any CAFC 2026 docket, appeal, or ITC/PTAB proceeding involving US 5,878,231. Details and caveats are at the end.

1. Bibliographic data

Note on number collisions. The string "5878231" also appears as (a) a U.S. trademark Registration No. 5878231 for the mark MAGIC CITY (casino/entertainment services, Classes 38/41), and (b) a Japanese patent number 特許第5878231号 (a wastewater-treatment apparatus). Neither is US 5,878,231 A. These are unrelated identifiers and I have not treated them as the same subject matter.

2. Abstract (as issued)

A system for screening data packets transmitted between a protected network (e.g., a private network) and another network (e.g., a public network). A dedicated computer is provided with three types of network ports: one to the private network, one to the public network, and one to a proxy network containing a predetermined number of hosts/services, some of which may mirror a subset of the private network's hosts. The proxy network is isolated from the private network so it cannot serve as a "jumping-off point" for intruders. Packets are filtered on the basis of their contents, state information, source/destination, and other criteria, and actions are taken accordingly: pass through (with or without alteration of data, IP address, etc.), drop (with or without an error message), or divert to a proxy host that performs some or all of the intended destination host's functions. Because packets pass without the addition of any network address pertaining to the screening system, the system is not identifiable as an IP entity and is therefore harder for intruders to target.

The specification adds that the screen is "signatureless": it preferably has no IP address at all, can interpret IP but is configured not to respond to IP requests, and therefore is not reachable by trace-route, ping, finger, etc. It also notes it is not a bridge or router, and requires no modification to either connected network.

3. Plain-language overview of the independent claims

There are two independent claims: claim 1 (method) and claim 7 (system); claims 2–6 depend from 1 and claims 8–12 depend from 7.

Claim 1 — Method (independent)

A method for inhibiting targeting of an "addressless" screening system coupled between a first and second computer network, comprising:

1. Receiving at the addressless screening system at least one data packet directed from the first network to the second, the packet having a source address identifying the first network and a destination address identifying the second network — with the addressless screening system being independent of the first network;
2. Inspecting the packet based on a predetermined criterion;
3. If the criterion is met, passing the packet through to the second network; and
4. If the criterion is not met, discarding the packet while preventing any response by the addressless screening system to the first network.

In everyday terms: a firewall-like device that has no address of its own sits invisibly on the wire; it reads each passing packet against a rule, forwards packets that comply, and silently swallows those that don't — crucially, without ever answering back, so the outside party gets no clue the device exists.

Claim 7 — System (independent)

A protection system for inhibiting targeting of an addressless screening system coupled between first and second networks, the screening system having a processor, a memory storing instruction modules executable by the processor, a first network interface to the first network and a second network interface to the second network (again independent of the first network). The protection system comprises:

• a first module configured to receive at least one data packet directed from the first network to the second, the packet including a source address identifying the first network and a destination address identifying the second network;
• a second module configured to inspect the packet based on a predetermined criterion;
• a "third" module configured to pass the packet through to the second network if the criterion is met; and
• a "third" module (so labeled in the printed claims — see caveat below) configured to discard the packet while preventing any response by the screening system to the first network if the criterion is not met.

In everyday terms: the same idea expressed as an apparatus — a processor plus stored program modules that receive, test, forward, and silently drop packets.

Literal-text caveats (I am not auto-correcting these):

• In claim 7, the "third said module" label is used twice — once for the passing function and once for the discarding function — and there is no "fourth module." As printed, that is a claim-drafting anomaly that may matter for claim construction or validity; whether a certificate of correction addresses it is outside the text I have.
• Claim 4 recites inspecting "a state of the connection between a source in the first network and a destination in the screening system" (not "in the second network"), which is a notable wording choice worth flagging.
• The independent claims recite "addressless" screening system; "addressless" is not given a formal definitional section, though the specification repeatedly states the screen has no IP/network address and does not respond to IP requests.
• Claim 1's text says the addressless screening system is "independent of the first computer network"; the abstract's framing (proxy network isolated from the private network) is consistent with that.

Dependent claims at a glance

• 2 / 8: inspection based on source address, destination address, source port, and/or destination port.
• 3 / 9: inspection based on the type of requested operation.
• 4 / 10: inspection based on connection state.
• 5 / 11: inspection based on time of day the operation is requested.
• 6 / 12: inspection based on whether the source is at an expected network location (the spec explains a packet whose source is a private-network host arriving on the public-network interface indicates possible address spoofing, and should be dropped without reply).

4. Litigation / docket search and uncertainty

• CAFC 2026 dockets: I found no Federal Circuit docket, oral-argument calendar entry, or notice of docketing for 2026 that references US 5,878,231. A search of the Federal Circuit's public March 2026 argument calendar surfaced unrelated captions; no match.
• USPTO / PTAB / TTAB: No IPR, PGR, or reexamination of US 5,878,231 appeared. The number did appear in TTAB proceedings, but in a trademark context (Registration No. 5878231, mark MAGIC CITY), which is a different register and a different property right.
• US district courts: No infringement suit asserting US 5,878,231 surfaced in my searches. The patent does appear as prior art in other parties' prosecution files (e.g., PCT search reports citing US 5,884,025 / US 5,878,231 against later firewall applications, and it was listed among references in the VirnetX-family patents such as US 8,904,516).
• Practical context: the patent's term ran to 2015‑05‑18, so a live 2026 infringement appeal is unlikely, though an appeal of a long-pending case or a collateral validity challenge is not categorically impossible.

Uncertainty statement: I cannot assert with high confidence that no 2026 CAFC activity exists; my conclusion is limited to what these searches returned. Commercial docket aggregators (Docket Alarm, UniCourt, CourtListener/RECAP) can lag or omit cases. A definitive check would require a PACER query on the patent number and a Federal Circuit docket search on "5,878,231," neither of which I can execute directly here. I also cannot confirm whether any certificate of correction has issued for the claim-numbering anomaly noted above.

I'll research litigation involving US Patent 5878231 specifically. Let me search multiple sources.

Let me search more targeted litigation databases.

Let me check litigation-specific databases.

Litigation Search Results for US Patent 5,878,231

Bottom line: I found no known litigation involving US Patent 5,878,231.

What the searches returned (and why it matters)

Searches of litigation-oriented sources (Unified Patents portal, RPX/insight.rpxcorp.com, Stanford NPE database, CourtListener, Justia, Docket Alarm, PTAB/USPTO PTACTS) did not surface any district court case, ITC action, PTAB proceeding, or Federal Circuit appeal in which US 5,878,231 was asserted, challenged, or otherwise at issue. The "hits" for the number were almost all false positives that must be flagged explicitly given your instruction to interpret identifiers literally and not auto-correct:

What US 5,878,231 actually is

Confirming the target so there is no ambiguity: US 5,878,231 ("System for packet filtering of data packets at a computer network interface"), inventors Baehr et al., original assignee Sun Microsystems, Inc., current assignee Oracle America, Inc. It is a divisional of US Application 08/444,351 (which issued as US 5,802,320), filed Feb. 4, 1997, priority date May 18, 1995, and it expired May 18, 2015 (family: US 5,802,320; US 5,878,231; US 5,884,025; EP 0743777; JP H09224053; SG 73981).

Important caveats

• I could not conclusively verify a negative. My searches reached the step limit before I could directly query the Unified Patents case list (https://portal.unifiedpatents.com/litigation/caselist), PACER, or Docket Navigator with a guaranteed complete result set. The absence of hits is evidence of no litigation, but it is not proof, particularly for (a) older pre-2000 cases that may not be digitized in free databases, and (b) cases where the patent was asserted but the public docket text is not indexed by free sources.
• No IPR/PGR/CBM was found for this patent — consistent with its 1995 priority date and 2015 expiration, which would make most AIA post-grant challenges time-barred or unavailable.
• Because the patent expired in 2015 and its subject matter (an addressless "signatureless" packet-screening firewall) predates the modern NPE assertion wave, it is plausible — though not proven here — that it was never asserted in litigation.

Recommendation: To close the verification gap, run a paid/authoritative query on Docket Navigator or Lex Machina (Patent tab → "5,878,231"), and a PACER full-text search in the specific districts where Sun/Oracle firewalls were challenged. If you'd like, I can attempt additional targeted searches (e.g., "Oracle" + "5,878,231," or the sibling patents 5,802,320 / 5,884,025, which may have been asserted even if the '231 was not) on a follow-up run.