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What are the flags in iptables-a forward-p tcp?
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.
Is the TCP flag the same as fin?
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.
What’s the problem with fragments in iptables?
The problem with fragments is that the initial fragment has the complete header fields (IP + TCP, UDP and ICMP) to examine, but subsequent packets only have a subset of the headers (IP without the additional protocol fields).
When to use mask Comp in TCP Flags?
[!] –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.
What causes a TCP / IP reset ( RST ) flag to be?
It’s hard to give a firm but general answer, because every possible perversion has been visited on TCP since its inception, and all sorts of people might be inserting RSTs in an attempt to block traffic. (Some ‘national firewalls’ work like this, for example.)
Why does my OS keep sending RST Flags?
OS is doing the resource cleanup when your process exit without closing socket. In your case, it sounds like a process is connecting your connection (IP + port) and keeps sending RST after establish the connection. In most applications, the socket connection has a timeout.
Why does my router send out a RST?
A ‘router’ could be doing anything – particularly NAT, which might involve any amount of bug-ridden messing with traffic… One reason a device will send a RST is in response to receiving a packet for a closed socket.