On Wednesday 02 February 2011 11:26 PM, Grant Taylor wrote:
On 2/2/2011 4:01 AM, Srinivasa T N wrote:
I am using ipt_NETFLOW 1.7 on my RHEL 6 (2.6.32) box. Now if I want to
accept packet destined for some port and at the same time I want it to
be accounted also, then I have to use the following rules:
I take it that the accounting you want is more than the simple packet /
byte counters that already exist.
But how will I have access to the counters from my user land app?
iptables -A INPUT --dport <portnum> -j NETFLOW
iptables -A INPUT --dport <portnum> -j ACCEPT
This makes that every packet that I accept should have two rules (one
for accepting and one for accounting). Don't you people think that it
will increase the number of rules a packet has to traverse? Or is my
understanding wrong?
You could do something like this:
iptables -N myChain
iptables -A myChain -j NETFLOW
iptables -A myChain -j ACCEPT
iptables -A INPUT --dport <portnum> -j myChain
Doing this will reduce the number of matches that have to be performed
and allow the (sub)chain to simply apply actions to the packets.
This might seem like over kill with your simple example, but when you
start putting multiple matches on each rule, or have more actions in
sequence (i.e. LOG) you start gaining more quickly. Further if you have
other rules that are matching other packets, they will not have to
traverse the condition that they will not match more than one time.
IPTables gives you a skeleton that you can do a lot of different things
in. It's really up to you how you put it together and how you optimize
rule traversal.
In some ways I could liken IPTables (and brethren) to a simple
programming language. As such, it's not the language its self that is
the limitation, just your imagination on how you use said language. :-)
Grant. . . .
--
Regards,
Seenu.
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