about mtu

udp2raw introduces it's own header for encryption, anti-replay and multiplex. As a result you have to decrease the MTU at upper level to "make room" for the extra overhead. (By the way, this is not only for udp2raw, this happens for almost all tunnels)

Since udp2raw itself doesn't have user space packet splitter, you have to tune the MTU at upper level appliation (for example: openvpn, wireguard, kcptun) to make sure they don't send packet too large for udp2raw.

However, if you are not happy with this or your upper level application doesn't allow you to tune MTU, there is indeed a way to by pass the MTU limitation, see https://github.com/wangyu-/udp2raw/wiki/bypass-mtu-limitation