[Click] About checksum computation ?

[yacine.djemaiel]

Hi Beyers,
Thanks for your help, i will modify this field and i will
check again.
I have modified it because i have in my mind the update
checksum method   defined in app/ftpportmapper.cc which uses
ip_len.

Thanks again Beyers


> 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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