Re: What does RELATED and ESTABLISHED really mean.

[Jamie Pratt <jamie@nucdc.org>]

... straight from the packet-filtering how-to: ( 
http://www.netfilter.org/documentation/HOWTO//packet-filtering-HOWTO.txt  )

  NEW
         A packet which creates a new connection.


      ESTABLISHED
         A packet which belongs to an existing connection (i.e., a reply
         packet, or outgoing packet on a connection which has seen
         replies).


      RELATED
         A packet which is related to, but not part of, an existing
         connection, such as an ICMP error, or (with the FTP module
         inserted), a packet establishing an ftp data connection.


regards,
jamie

Michael Gale wrote:

> Hello,
> 
> 	I have been reading many netfilter documents and books, they all talk about related and established connections. To use them for FTP connections and to simplify rule sets.
> 
> But none explain exactly what an ESTABLISHED or RELATED connection is ?
> 
> Here are my definitions ... please let know if these are correct :)
> 
> ESTABLISHED - This allows return packets from a connection and all proceeding packets.
> 
> Example -- you have a web server on the DMZ network.
> you have the following iptables rules.
> 
> $IPT -t nat -A POSTROUTING -i $EXT_FACE -d X.X.X.X -j SNAT --to-destination 172.16.0.5
> 
> $IPT -A FORWARD -i $EXT_FACE -o $DMZ_FACE -d 172.16.0.5 -p tcp --sport 1024:65535 --dport 80 -m state --state NEW,ESTABLISHED -j ACCEPT
> 
> $IPT -A FORWARD -i $DMZ_FACE -o $EXT_FACE -s 172.16.0.5 -p tcp --sport 1024:65535 --dport 1024:65535 -m state --state ESTABLISHED -j ACCEPT
> 
> This only allow a tcp connection to be setup between a out side client and a web server on the DMZ. It also only allows the web server to respond to a TCP connection on port 80 and does NOT allow the web server to initiated a outgoing TCP connection.
> 
> If I used related it would allow the web server to make a out going TCP connection to the server that made the initial inbound connection  ?
> 
> Sorry -- I hope I explained this well.
> 

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