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Re: Network Variables
From: waldo kitty <wkitty42 () windstream net>
Date: Thu, 02 May 2013 15:00:04 -0400

On 5/2/2013 13:23, Seth Dunn wrote:
So now my question comes, since you were wondering about the rule I was
using.
This is my rule::
not net 10.10.0.0/24 and dst host 10.75.45.1&&  dst port 80 or not net
10.30.0.0/24 and dst host 10.75.45.1&&  dst port 80

ok, i'm going to try to break this down and interpret your wants one section at 
a time...

By my understanding, and my desire to see happen is this.
Traffic from the network 10.10.0.0/24 going to http at 10.75.45.1 should
be ignored.

(net 10.10.0.0/24 and (host 10.75.45.1 and port 80))

Also, traffic from the network 10.30.0.0/24 going to http at 10.75.45.1
should be ignored.

(net 10.30.0.0/24 and (host 10.75.45.1 and port 80))

All other traffic is still monitored.

the above should qualify your two wants... now, let's streamline them a bit to 
make it more legible...

first, let's combine the two source networks into one statement...

net (10.10.0.0/24 or 10.30.0.0/24)

now the destination host and destination port...

host 10.75.45.1 and port 80

then combine those two lines...

net (10.10.0.0/24 or 10.30.0.0/24) and host 10.75.45.1 and port 80

and lastly negate the whole thing by enclosing it in parens with 'not' on the 
outside...


not (net (10.10.0.0/24 or 10.30.0.0/24) and host 10.75.45.1 and port 80)


plug that line into your bpf with the double quotes or whatever you need to wrap 
around it and see what happens ;)


FWIW: this was minimally tested on my network via tcpdump and manually checking 
the pcap with wireshark...

NOTES:
1. using 'src net' and 'dst host' plus 'dst port' resulted in only the traffic 
/to/ the server being ignored but all the traffic from the server was seen...

2. removing the 'src' and 'dst' designators denotes all traffic in both 
directions that fits the mask (if i can use that term to describe this object)...

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