aeron-io/aeron · error · IllegalArgumentException

unsupported congestion control : cc=

Error message

unsupported congestion control : cc=${ccStr}

What it means

DefaultCongestionControlSupplier.newInstance throws IllegalArgumentException when the requested congestion control strategy (cc parameter from the channel URI or configured class name) does not match any supported implementation.

Solutions

1. Use one of the supported values: CongestionControl classes shipped with the driver (e.g. StaticWindowCongestionControl, CqrCongestionControl)
2. Provide a custom CongestionControlSupplier that recognizes your strategy instead of relying on the default
3. Check the exact fully-qualified class name including package

Example fix

// before
ctx.congestionControlStrategy("MyCc"); // unsupported -> IllegalArgumentException
// after
ctx.congestionControlStrategy(StaticWindowCongestionControl.class.getName());

Set<String> supported = Set.of(StaticWindowCongestionControl.class.getName(), CqrCongestionControl.class.getName()); if (!supported.contains(ccStr)) throw new IllegalArgumentException("unsupported cc=" + ccStr);

When it happens

Trigger: Setting context.congestionControlStrategy(...) or channel URI cc= parameter to a class name other than the supported CqrCongestionControl/StaticWindowCongestionControl implementations.

Common situations: Typo in the fully-qualified class name, using a congestion control from a different Aeron version or fork, or copy-pasting a cc= value that the default supplier does not know.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• invalid port value
• :low port value must be lower than high port value
• mtuLength= <= HEADER_LENGTH=
• mtuLength= > initialWindowLength=
• mtuLength= > MAX_UDP_PAYLOAD_LENGTH=

AI-assisted analysis of aeron-io/aeron@6d60124e15 (2026-09-12). Data as JSON: /api/errors/ddb88656b5297956. Report an issue: GitHub.

Appendix: source

Thrown at aeron-driver/src/main/java/io/aeron/driver/DefaultCongestionControlSupplier.java:89

                countersManager);
        }
        else if (CubicCongestionControl.CC_PARAM_VALUE.equals(ccStr))
        {
            return new CubicCongestionControl(
                registrationId,
                udpChannel,
                streamId,
                sessionId,
                termLength,
                senderMtuLength,
                controlAddress,
                sourceAddress,
                nanoClock,
                context,
                countersManager);
        }

        throw new IllegalArgumentException("unsupported congestion control : cc=" + ccStr);
    }
}

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