iptables - -syn

yawe_frek · 12-01-2006, 12:04 PM

hi guys ,

I am writing my rc.packetfilter scripts, and i was wondering if i needed any rules like these there.

iptables -A INPUT -p tcp --syn -i eth0 --dport 23 -j ACCEPT.(what will a rules like this do)

The problem i am having now is that i seem not to understand fully waht the syn does. pls i need more clarification on how this is use and basiclly what is does.

Thanks

musicman_ace · 12-02-2006, 04:56 AM

First off, DO NOT use telnet.

But that rule would be explained like this:

Code:

Append a rule for incoming (Traffic coming to this server)
When they are TCP syn packets
on eth0
destined for port 23
Accept them.

You may want to limit rate those, because I could syn flood you and you would be victim of a DoS. Use port 22 which is secure shell.

Mara · 12-02-2006, 03:26 PM

SYN packet is the first one that comes when a connection is established (well...at the time of syn there's no connection yet). If you want to allow a connection to a specific port, you need to allow such packets pass. There's no need to use --syn if you already allow --state NEW.