Netgraph node to replace packet contents?

[Norberto Meijome]

On Sun, 26 Aug 2007 15:54:43 +0300
Alexander Motin <mav at FreeBSD.org> wrote:

> Hi.
> 
> Norberto Meijome wrote:
> > is there any already existing  Netgraph node that would allow me to replace bytes in the data part of a packet?  I'm talking about generic "foo" for "BAR" replacement, though different lengths  would be good too.
> 
> There is no such node.
> 
> This is not an easy task to alter some abstract packet. Even in 
> simpliest case you should take into account TCP/UDP checksumms. 
Yes, of course.

> There 
> could be problems with fragmented packets. In more complicated cases may 
> be required other modifications.

yes..i had thought of this

> 
> To replace string with different length one you should also correct 
> packet length. It is possible for UDP (except for the not first packet 
> fragments), but for TCP it is probably completely impossible without 
> doing complete TCP proxying to modify sequence numbers.

yes, TCP keeps rearing its problematic head ;) 

Anyway, thanks a lot for the insights :)
B

_________________________
{Beto|Norberto|Numard} Meijome

Law of Conservation of Perversity: 
  we can't make something simpler without making something else more complex

I speak for myself, not my employer. Contents may be hot. Slippery when wet. Reading disclaimers makes you go blind. Writing them is worse. You have been Warned.