dotnetcore/CAP · error · Exception

no available mac found

Error message

no available mac found

What it means

A hardware-environment guard in SnowflakeId's MAC-based worker-id generation: GenerateWorkerIdBaseOnMac iterates network interfaces excluding virtual and loopback adapters, and when none qualifies (e.g. containers/VMs exposing only virtual NICs, or no network hardware) the method reports that no usable MAC address exists to derive a worker id from. It is raised inside worker-id auto-detection, not during message flow.

Solutions

1. Set SnowflakeIdOptions.WorkerId explicitly to a stable value in the 0–1023 range so MAC detection is never needed.
2. In containerized environments where only virtual adapters exist, prefer explicit configuration or an external id allocator over MAC-based auto-detection.

When it happens

Trigger: Thrown at src/DotNetCore.CAP/Internal/ISnowflakeId.Default.cs:162 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of dotnetcore/CAP@e52b8508e5 (2026-09-14). Data as JSON: /api/errors/444c5728b4db2745. Report an issue: GitHub.

Appendix: source

Thrown at src/DotNetCore.CAP/Internal/ISnowflakeId.Default.cs:162

        }
        catch
        {
            return GenerateRandomWorkerId(maxWorkerId);
        }
    }

    /// <summary>
    /// use lowest 10 bit of available MAC as workerId
    /// </summary>
    /// <returns>workerId</returns>
    private static long GenerateWorkerIdBaseOnMac()
    {
        NetworkInterface[] nics = NetworkInterface.GetAllNetworkInterfaces();
        //exclude virtual and Loopback
        var firstUpInterface = nics.OrderByDescending(x => x.Speed).FirstOrDefault(x =>
            !x.Description.Contains("Virtual") && x.NetworkInterfaceType != NetworkInterfaceType.Loopback &&
            x.OperationalStatus == OperationalStatus.Up);
        if (firstUpInterface == null) throw new Exception("no available mac found");
        var address = firstUpInterface.GetPhysicalAddress();
        var mac = address.GetAddressBytes();

        return ((mac[4] & 0B11) << 8) | (mac[5] & 0xFF);
    }

    /// <summary>
    /// randomly generate one as workerId
    /// </summary>
    /// <returns></returns>
    private static long GenerateRandomWorkerId(int maxWorkerId)
    {
        return new Random().Next(maxWorkerId + 1);
    }
}

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