Network telescopes (aka darknets) collect unsolicited Internet traffic (aka Internet background radiation or IBR), which includes benign and malicious scanning as well as artifacts of spoofed denial-of-service attacks and misconfigured software and hosts. Analysis of this traffic has revealed macroscopic insights into security-related events and global network dynamics such as outages. Operating a large-scale network telescope is challenging but often taken for granted, more so than in more mature scientific disciplines. We offer the first study documenting our experiences operating the UCSD Network Telescope, the largest and longest-operating network telescope supporting scientific research. We provide background on the history of the telescope, and focus on increasing operational challenges as the underlying network evolves. We develop and apply techniques to leverage third-party scanning activity to validate the integrity of the data, and to discover misconfigurations in the instrumentation. These insights are crucial for understanding measurement results, which we illustrate using concrete examples. We discuss how our findings generalize to support the expanding ecosystem of other passive techniques, such as honeypots, to track security phenomena.

In this paper, we present a detailed performance analysis of QUIC instant~ACK, a standard-compliant approach to reduce waiting times during the QUIC connection setup in common CDN deployments. To understand the root causes of the performance properties, we combine numerical analysis and the emulation of eight QUIC implementations using the QUIC Interop Runner. Our experiments comprehensively cover packet loss and non-loss scenarios, different round trip times, and TLS certificate sizes. To clarify instant ACK deployments in the wild, we conduct active measurements of 1M~popular domain names. For almost all domain names under control of Cloudflare, Cloudflare uses instant ACK, which in fact improves performance. We also find, however, that instant ACK may lead to unnecessary retransmissions or longer waiting times under some network conditions, raising awareness of drawbacks of instant ACK in the future.

In this paper, we revisit the performance of the QUIC connection setup and relate the design choices for fast and secure connections to common Web deployments. We analyze over 1M Web domains with 272k QUIC-enabled services and find two worrying results. First, current practices of creating, providing, and fetching Web certificates undermine reduced round trip times during the connection setup since sizes of 35% of server certificates exceed the amplification limit. Second, non-standard server implementations lead to larger amplification factors than QUIC permits, which increase even further in IP spoofing scenarios. We present guidance for all involved stakeholders to improve the situation.