Impact of PTB Message Usage on Path MTU Discovery for QUIC

A data sender in an IP-based network is only capable of efficiently using a network path if it knows the packet size limit of the path, i.e., the Path Maximum Transmission Unit (PMTU). An IP router that cannot forward and must drop an oversized packet should notify the sender with a Packet Too Big (PTB) message, which contains the maximum packet size it can forward. A transport protocol supporting a discovery to determine the PMTU may use PTB messages. However, for the transport protocol QUIC (e.g., used by HTTP/3), we identified only a few implementations that determine the PMTU and none of them process PTB messages. In this paper, we present results from simulations that show how much a QUIC sender using PMTU discovery benefits from processing PTB messages, which includes a result that outlines the benefit of determining the PMTU in general. Further, we analyze the risk of using PTB messages and describe a way to protect against potential attacks with forged PTB messages.