Re: Splitter

[syedk <syedk@intotoinc.com>]

hi ananth,
  yes u can directly send it to other interface...
but be very careful in this : u need to take care of lot of things
otherwise u may face lot of kernel panics:
1) u shud return NF_STOLEN; in the PRE_ROUTING hook... otherwise the
dev_queue_xmit will try to free the sk_buff (which might be already
freed if u use NF_DROP)...
2)u need to fill( or rather change existing ones) the relevant
information in the sk_buff...  that might include the
  i) source and destination address in the IP ..
  ii) changing the pkt_type to PACKET_OUTGOING,
  iii) u also need to take care of changing datalink layer stuff in
sk_buff.. for example if packet came on ppp or loopback and u want to
redirect it to ethernet interface.....

  all u need to care of is this : it shud be a correct sk_buff while
xmiting it....
 probably u wont succeed first time itself .... u may find some problems
or worst some crashes... but u will succeed finally...

Better read this document: 
http://uqconnect.net/~zzoklan/documents/netfilter.html

i hope this would help...

best regards
Syed SK

On Tue, 2004-03-23 at 17:24, K.Anantha Kiran wrote:
> Hi,
>   Whenever we receive a packet( let it is stored in skb), can we directly 
> change the skbuff->dev and call dev_queue_xmit(skbuff) without undergoing 
> any processing in this system. That means this will simply take one packet and 
> keep it in another interface( for suppose there are no packets destined 
> for this system) . Doing this will cause any problems? 
> 
> 
> 
> On 23 Mar 2004, syedk wrote:
> 
> > Date: 23 Mar 2004 17:08:20 +0530
> > From: syedk <syedk@intotoinc.com>
> > To: K.Anantha Kiran <ananth@cse.iitk.ac.in>
> > Cc: Jad Saklawi <Jad@Saklawi.info>, linux-c-programming@vger.kernel.org
> > Subject: Re: Splitter
> > 
> > you can look into dev_queue_xmit(sk_buff) function in net/core/dev.c
> > 
> >  sk_buff->dev  has the information abt the device (can be any interface
> > registered using register_netdevice() for that matter)...
> > 
> > dev_queue_xmit just transfers the sk_buff for the device for
> > delivery....
> > 
> > I feel the best way to solve your problem would be use NF_IP_PRE_ROUTING
> > hook of netfilter by which u get all packets ( even before any routing
> > decisions has been made : that is what u wanted RIGHT??) and then call
> > dev_queue_xmit function by setting the sk_buff->dev as whatever
> > interface u wish to redirect....
> > 
> > I hope this would help....
> > 
> > Best regards
> > syed sk
> > 
> > 
> > On Tue, 2004-03-23 at 15:09, K.Anantha Kiran wrote:
> > > Hi,
> > >  Thanks a lot for ur guidance.
> > >  I am following the same files(i mean NET directory).But i am facing 
> > > following problem.
> > >  " where the output interface variable (rtable->key->oif) is changed to 
> > > the index of interface through which packet has to go out. In the function 
> > > /net/route.c ip_route_input_slow() they are setting it to 0 what is it 
> > > mean.
> > > 
> > > 	When a packet has to be put on to an interface what are the fields 
> > > will it use to decide that( in skbuff structure).
> > > 
> > > Thanks 
> > > regards,
> > > K. Anantha kiran
> > > 
> > > 
> > > On Mon, 22 Mar 2004, Jad Saklawi wrote:
> > > 
> > > > Date: Mon, 22 Mar 2004 09:41:22 +0200
> > > > From: Jad Saklawi <Jad@Saklawi.info>
> > > > To: K.Anantha Kiran <ananth@cse.iitk.ac.in>
> > > > Cc: linux-c-programming@vger.kernel.org
> > > > Subject: Re: Splitter
> > > > 
> > > > K.Anantha Kiran wrote:
> > > > 
> > > > >Hi,
> > > > > Thanks for ur suggetsion.
> > > > > But we are not clear about the sentece "re invent the loop".
> > > > > Can u give clear explanantion about the "iptables" solution.
> > > > > IMP: Our machine should not work like a router.I should be able to decide 
> > > > >to which interface i want to redirect to , on the fly for each packet 
> > > > >using a HASH like functions.
> > > > >  
> > > > >
> > > >  It`s your choice then, check out net/core/dev.c net/core/dv.c 
> > > > net/ipv4/tcp_input.c net/ipv4/tcp_output.c net/ethernet/eth.c You have 
> > > > to take a look at the whole net directory and modify accordingly. I 
> > > > doubt you will be able to do any thing. Any way good luck!!!
> > > > 
> > > > Greets,
> > > > Jad
> > > > 
> > > 
> > > -
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