mjhjmtu

Question 1: are the following rules equal?

iptables -t raw -A PREROUTING -p tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG NONE -j DROP
iptables -t raw -A PREROUTING -p tcp --tcp-flags ALL NONE -j DROP

Question 2: are the following rules equal?

iptables -t raw -A PREROUTING -p tcp --tcp-flags FIN,SYN FIN,SYN -j DROP
iptables -t raw -A PREROUTING -p tcp --tcp-flags SYN,FIN SYN,FIN -j DROP

I'm new to iptables and I'm a bit confused because some tutorials suggest to use those four rules.

Yes, they are for both the questions.

ALL is the same as FIN,SYN,RST,PSH,ACK,URG.

Check out the man iptables-extensions command on --tcp-flags which is used when the TCP protocol is used: -p tcp.

[!] --tcp-flags mask comp
 Match when the TCP flags are as specified. The first argument
 mask is the flags which we should examine, written as a comma-
 separated list, and the second argument comp is a comma-sepa‐
 rated list of flags which must be set. Flags are: SYN ACK FIN
 RST URG PSH ALL NONE. Hence the command
 iptables -A FORWARD -p tcp --tcp-flags SYN,ACK,FIN,RST SYN
 will only match packets with the SYN flag set, and the ACK, FIN
 and RST flags unset.