WSOU Investments LLC (Brazos) against F5, Inc., decided April 7, 2025

This Federal Circuit opinion addresses an appeal by WSOU Investments LLC (Brazos) against F5, Inc. regarding a patent for network traffic distribution. The dispute centered on the interpretation of the term "master device" within the patent claims. The district court had adopted Brazos's proposed construction during claim construction but later granted summary judgment of noninfringement to F5. Brazos appealed this decision, arguing for a new interpretation of "master device" that differed from its earlier stance. The Federal Circuit found that Brazos had forfeited this new argument by not presenting it to the district court. Consequently, the appellate court affirmed the district court's summary judgment, holding Brazos to its previously advocated claim construction.

Case Name and Citation: WSOU INVESTMENTS LLC, DBA BRAZOS LICENSING AND DEVELOPMENT v. F5, INC., FKA F5 NETWORKS, INC., 2023-1427, 2025-1505 (Fed. Cir. April 17, 2025) (nonprecedential). Download the opinion here.

Court: United States Court of Appeals for the Federal Circuit

Issue: Did the district court err in granting summary judgment of noninfringement in favor of F5, Inc.? Specifically, did Brazos Licensing forfeit its claim construction argument on appeal?

Holding: Yes. The Federal Circuit affirmed the district court's grant of summary judgment, finding that Brazos Licensing forfeited its appellate argument regarding the construction of the "master device" claim limitation because it presented a different interpretation on appeal than it did before the district court.

Background:

• Patent in Question: U.S. Patent No. 7,548,945, titled "System, Network Device, Method, and Computer Program Product for Active Load Balancing Using Clustered Nodes as Authoritative Domain Name Servers." The patent claims systems and methods for distributing network traffic across multiple devices in a cluster, where a "master device" plays a key role in selecting which device handles a client request.

• Technology Described: The patent addresses the problem of efficiently selecting a server from a group of servers associated with a single domain name. Traditional "DNS round-robin" methods could lead to issues like selecting unavailable or overloaded servers.

• Patented Solution: The ’945 patent proposes a cluster of devices acting as an authoritative name server. Each device in the cluster shares status information (e.g., load, active connections) with a designated "master device." This "master device," assigned an IP address as the authoritative domain name server, receives DNS queries, selects a device in the cluster based on the status information, and returns that device's IP address to the client. The patent specification also notes that "[t]he designation of master device may be transferred as necessary from one device to another device."

• Claim Language: Representative claims 1, 6, and 12 include the limitation of a "master device" which "is assigned an IP address corresponding to an IP address of an authoritative domain name server" and is configured to receive DNS queries, select a network device, and return its IP address.

• District Court Proceedings:Brazos sued F5 for infringement in the Western District of Washington.

• During claim construction, a dispute arose over the meaning of "a master device." Brazos argued it meant "a device in a cluster that is configured to select other device(s) at a given time" and that the patent "does not require ‘a single network device,’ as F5 proposes," emphasizing that "any device can serve as the master." F5 argued it meant "[a] single network device controlling the other devices in the same cluster," contending that "only one device at a time is the master."

• The district court adopted Brazos's proposed construction, stating: "While [F5] is correct that the patented technology contemplates there being only one master device in a cluster at a given time, any device in the cluster can serve as the master device, and the device playing the master role may change as needed." The court noted this flexibility was an improvement over the prior art.

• Following discovery, F5 moved for summary judgment of noninfringement, arguing that its product did not have the "interchangeability" of master device functionality among any device in the cluster, which F5 contended was required by the district court's claim construction.

• Brazos opposed, arguing that the claim construction did not require each device to be interchangeable, only that other devices could be designated as master.

• The district court granted summary judgment for F5, concluding that Brazos's interpretation "defies the plain language of the [claim-construction] order," which the court understood to require that "any device in a cluster can function as the master device at any given time." The court found no genuine factual dispute that F5's product lacked this capability.

Federal Circuit Analysis:

• Forfeiture of Claim Construction Argument: The Federal Circuit focused on whether Brazos had forfeited its claim construction argument on appeal. The court stated a "very strong rule forbidding an appellant to urge a construction on appeal that asserts a different claim scope from what it urged in the tribunal being reviewed."

• Brazos's Appellate Position: On appeal, Brazos argued that the district court erred in its claim construction and contended that "under the correct claim construction of the ‘master device’ phrase, once a cluster device has been selected as the master device, not even a single one of the other cluster devices need be available to be switched in to play the master role."

• Comparison with District Court Arguments: The Federal Circuit found that this appellate argument was not presented to the district court. The court emphasized that Brazos had previously argued that "the patent contemplates that any device can serve as the master" and that "any node in the cluster is generally capable of functioning as the master node."

• District Court's Understanding: The Federal Circuit noted that the district court explicitly adopted Brazos's argument about the flexibility and interchangeability of the master device role as the reason for choosing "a device" over F5's "a single device." The district court's claim construction order stated that "any device in the cluster can serve as the master device, and the device playing the master role may change as needed."

• Brazos's Post-Claim Construction Argument: Even after the claim construction order, when opposing summary judgment, Brazos argued that the claims "do permit other devices in the cluster to be designated as master at a given time," further reinforcing the idea of potential interchangeability, even if not a requirement for each device.

• No Basis for Excusing Forfeiture: The Federal Circuit found "no sound reason to excuse Brazos’s forfeiture." It highlighted the importance of timely and consistent presentation of claim construction positions for efficient litigation. The court also noted that Brazos "affirmatively led the district court to the position it now disowns."

• Lack of Alternative Arguments: The Federal Circuit pointed out that Brazos did not argue that summary judgment was improper under the district court's construction, nor did it request a remand for further proceedings based on a different construction.

• Support in the Specification: The court also referenced the patent specification, which states, "The designation of master device may be transferred as necessary from one device to another device," supporting the idea of the master role being transferable.

  
  

Conclusion:

The Federal Circuit affirmed the district court's grant of summary judgment of noninfringement. It held that Brazos Licensing had forfeited its claim construction argument on appeal by presenting a new interpretation of "master device" that contradicted its arguments before the district court. Because Brazos did not argue that F5 infringed under the district court's construction, and its new construction was forfeited, the appellate court found no basis to reverse the summary judgment ruling. The court emphasized the importance of consistently arguing claim construction positions throughout litigation.