[Click] About checksum computation ?

[Beyers Cronje]

Hi Yacine,

You have two options:

(A) Use SetIPChecksum element. If you only want to set certain packets then push those packets out a seperate output port which connects to SetIPChecksum element.
(B) You were using the ip packet length: ip_len, where only the ip header length is needed: ip_hl. From SetIPChecksum() element, correct code to set IP checksum:

  hlen = ip->ip_hl << 2;
  ip->ip_sum = 0;
  ip->ip_sum = click_in_cksum((unsigned char *)ip, hlen);

The above works in my code.

Regards

Beyers


-----Original Message-----
From: click-bounces at amsterdam.lcs.mit.edu
[mailto:click-bounces at amsterdam.lcs.mit.edu]On Behalf Of yacine.djemaiel
Sent: Monday, November 01, 2004 11:33 AM
To: bart.braem
Cc: click
Subject: Re: [Click] About checksum computation ?


I need to compute checksum only for some packets selected and
not for all traffic. If, i have not found a solution, i will
use this element.

Thanks Bart for your help


> Op maandag 1 november 2004 10:03, schreef u:
> > Hi,
> > i would like to compute checksum after modifying an ip header
> > field. I have followed set_cksum method (fromtcpdump.cc), but
> > i get all the time an incorrect ip header checksum. Lines of
> > code that i am using are :
> >
> Why not use the SetIPChecksum element? That's a fine element
that works 
> perfectly...
> 
> Bart
> _______________________________________________
> click mailing list
> click at amsterdam.lcs.mit.edu
> https://amsterdam.lcs.mit.edu/mailman/listinfo/click
> 

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