I use fwknop[0] on my servers. It does single-packet authorization rather than straight port knocking, which solves the replay issue. [0] https://www.cipherdyn

I use fwknop[0] on my servers. It does single-packet authorization rather than straight port knocking, which solves the replay issue. [0] https://www.cipherdyne.org/fwknop/ https://www.cipherdyne.org/fwknop/