Kali Linux package downloads exhibit latency spikes under concurrent APT requests

Kali Linux systems fetching packages from the official Ubuntu-based mirrors show a sharp latency increase once several concurrent apt or curl downloads are active, while single-threaded requests remain fast. The behavior suggests a mirror-side throttle, but the exact thresholds—number of simultaneous connections, bytes per second, or per-IP limits—are not documented in Kali or Ubuntu release notes.

This uncertainty matters for automated build pipelines and vulnerability-scanning workloads that rely on parallel package retrieval. Because the underlying mirror infrastructure is standard Ubuntu, the limiting configuration is not exposed to end users, making it difficult to distinguish mirror-side throttling from local network saturation or client-side queueing.

What concurrency threshold triggers the latency increase on Kali’s official mirrors? Is there a supported client-side setting to avoid the slowdown without changing mirrors or adding a caching proxy?