Constant MAX_UDP_PAYLOAD_IPV4 

pub const MAX_UDP_PAYLOAD_IPV4: usize = 65_507; // 65_507usize

Available on crate features std and udp only.

Largest UDP payload representable by ordinary IPv4.

This is an implementation ceiling, not a path MTU. Applications should normally send substantially smaller packets and perform path MTU discovery in the protocol layer when appropriate.