By the sharp speed plus firewall pit a bit ...

The server on the SS, plus the sharp speed acceleration.

Had never opened the firewall, yesterday found this too insecure, on the Ubuntu firewall

UFW Default policy intercepts all input and forward by default, allowing output

Also allows input policy-a ufw-before-input-m conntrack--ctstate related,established-j ACCEPT

The established represents a packet with an ACK SYN of 1, or all connections after the second handshake.

After the pit has come, with the sharp speed, the TCP packet will be modified, usually adding the Urg bit

such as: In=eth0 out= mac= src=8.8.8.8 dst=xx. Xx. Xx. XX len=60 tos=0x00 prec=0x00 ttl=56 id=45447 proto=tcp spt=53 dpt=58310 window=28960 res=0x00 ACK SYN URGP=0

So, this package is recognized as invalid ... It was intercepted.

After you close the sharp speed ...

　　

By the sharp speed plus firewall pit a bit ...