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Old 09-08-2005, 01:10 AM   #1
wangjinyi
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about the ip packet intercepting


I want to do something in this way:

All ip packets sent to a host A will be captured in A before the packets
are passed to the high layer, i.e. the TCP or APP.

And, all ip packets sent from A to some other host will be captured in
low layer in A, i.e. Link layer, then the packet will be transferd.

that means i can do something before a packet is passed to the TCP or APP and the same as before it is passed to the Link layer.

I think, if i rewrite the ip stack in kernel, i can do it.
but, is there a simple method to do this? for example, writing a module or a program, when i load the module or run the program, all will be ok.

it is seem to be more difficult. and what is about the windows. i can't rebuild the windows.

would you like to give me some suggestions?
 
Old 09-08-2005, 01:40 AM   #2
jlliagre
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What about looking some firewall source code and see how it is done ?
 
Old 09-08-2005, 01:47 AM   #3
wangjinyi
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good idea. but that is a different way.

i want do it on the source host, not a intermedia host.

How?
 
Old 09-08-2005, 04:15 AM   #4
jlliagre
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This is not a different way, a firewall can sit anywhere, on the server, the client, or a machine between.
 
Old 09-08-2005, 07:27 PM   #5
wangjinyi
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you are right, and that is a very good way to do this,
i am so sorry for my ignorantness.

and, would you like to give me some directions about how to
get some source code about a firewall.


thx any way.
 
Old 09-09-2005, 01:15 AM   #6
jlliagre
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You should first tell on what O/S you want your intercepting code to run.
Then I'm sure google will help you finding source code.
 
Old 09-09-2005, 01:35 AM   #7
wangjinyi
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I have found one from google.

So kind of you.
 
Old 09-13-2005, 09:48 PM   #8
wangjinyi
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I have read some firewall source code of linux, but almost of them base on
the linux utility iptables, that means i can't change any ip packet and only
can make a decision of droping of accepting.

that is so discouraged.

is there one which does not base on iptables? where to get it?
 
Old 09-14-2005, 12:07 AM   #9
jinxcat
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Try googling for "Roll your own firewall with netfilter", it's a Linuxjournal article that does something similar.

Also, I believe phrack.... 55 was it? had something on the matter too...
 
  


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