Latency and Privacy in Lightning

The discussion revolves around the behavior of packet fragmentation and reassembly, particularly in the context of syncing a bitcoind node on a MacBook. It is observed that packets larger than 1500 bytes are being fragmented and reassembled. This phenomenon is attributed to the Maximum Transmission Unit (MTU) limitation, which is largely consistent across different operating systems despite its legacy origins. The 1500 byte MTU limitation's history and implications are further explored through a provided link, which offers insight into why this standard was established.

Recent developments in the field, as outlined by RFC8900 and RFC4963, highlight the complexities and challenges associated with IP packet fragmentation and reassembly. RFC8900, written in 2020, delves into issues such as Path MTU Discovery and its limitations, including the lack of authentication and potential for rate-limiting or black-holing. It also compares IPv4 and IPv6, noting IPv6’s reduced vulnerability to third-party IP reassembly attacks and the recommendation against relying on IP fragmentation due to its fragility.

RFC4963, from 2007, focuses on the mechanics of IP reassembly, mentioning IPv4's use of a 16-bit ID field for assembling fragments based on source, destination, protocol, and identifier. It discusses the implications of packet lifetimes, reassembly timeouts, and the potential for mis-association of overlapping IP packets, which can lead to errors bypassing checksum validations. The document recommends application-layer cryptographic integrity checks as a safeguard, a practice already adopted in Bitcoin and Lightning networks.

The conversation also touches upon the practical aspects of dealing with packet fragmentation in real-world applications, mentioning the potential for A/B testing on mainnet nodes by alternating between padded and unpadded packets to observe effects on latency. This approach underscores the difficulty of obtaining concrete data on the internet's handling of fragmentation and reassembly. The mention of other applications' strategies, like Tor's, in managing large data transmissions suggests a broader interest in optimizing network communication despite inherent challenges.

In summary, the exchange encapsulates the technical intricacies of packet fragmentation and reassembly within the broader context of network communication and security. It underscores the ongoing evolution of standards and practices designed to mitigate the limitations and vulnerabilities associated with these processes, reflecting a commitment to enhancing the efficiency and integrity of digital communications.