Reference RFC1122: https://datatracker.ietf.org/doc/html/rfc1122 ---------------------------------------------- 4.1.3 SPECIFIC ISSUES 4.1.3.1 Ports If a datagram arrives addressed to a UDP port for which there is no pending LISTEN call, UDP SHOULD send an ICMP Port Unreachable message. Signed-off-by: chao.an <anchao@xiaomi.com>