Constant pnet::packet::tcp::TcpFlags::ECE

pub const ECE: u16 = 64; // 0x0_040u16

ECE – ECN-Echo has a dual role, depending on the value of the SYN flag. It indicates: If the SYN flag is set (1), that the TCP peer is ECN capable. If the SYN flag is clear (0), that a packet with Congestion Experienced flag set (ECN=11) in IP header received during normal transmission (added to header by RFC 3168).