TCP hole punching for Bitcoin nodes behind home NATs?

The discussion around improving network protocols for more effective data transmission has sparked interest in potentially integrating QUIC or developing a custom UDP-based transport within the core system. The proposal to utilize a UDP-based transport is driven by the advantages it may offer; however, there are significant challenges that need to be addressed. The current Peer-to-Peer (P2P) protocol employed is intricately stateful, incorporating many small state-dependent features. This inherent statefulness complicates any straightforward transition from TCP to UDP, as UDP's lack of built-in mechanisms for managing duplicates, dropped messages, and out-of-order deliveries could lead to functional disruptions.

Given these complications, the feasible options include adopting QUIC or creating a custom protocol wrapper that essentially replicates QUIC's functionality. QUIC already provides an established framework designed to handle such issues effectively, making it a strong candidate for adoption. However, the complexity and potential resource demands associated with implementing these changes pose a considerable challenge. There might not be sufficient justification for the effort and resource allocation required for such an overhaul when considering the trade-offs.

Despite these challenges, there remains optimism regarding the capabilities of TCP hole punching techniques. Although TCP hole punching is recognized as being more fragile and less robust compared to UDP hole punching, it might still deliver substantial benefits without the extensive modifications required by a shift to UDP-based protocols. This potential makes it an appealing interim solution while more durable and efficient methods are explored and developed.