So I tracked down the bug to a "feature" within the original fragroute
code. You can disable this by commenting out the following 3 lines in
src/fragroute/fragroute.c in fragroute_process() (around lines 72-74)
if (pkt->pkt_eth && htons(pkt->pkt_eth->eth_type) == ETH_TYPE_IP) {
ip_checksum(pkt->pkt_ip, len);
}
That should prevent the packets from having their checksums
recalculated prior to being fragged. After this, IPv4 checksums will
still be calculated for each IP fragment, but the layer 4 checksums
(TCP, UDP) will not be (assuming at least you have a recent version of
libdnet installed).
Anyways, this fix will be in the next release.
On Thu, Dec 16, 2010 at 9:35 AM, Aaron Turner <synfina...@gmail.com> wrote:
> That version is a bit out of date (3.4.4 is the latest), but I'm not
> aware of anything that would change that functionality since 3.4.1.
> If you get a chance, give 3.4.4 a try (it does fix other bugs) and
> I'll see about reproducing your problem and coming up with a fix in
> 3.4.5.
>
> --
> Aaron Turner
> http://synfin.net/ Twitter: @synfinatic
> http://tcpreplay.synfin.net/ - Pcap editing and replay tools for Unix &
> Windows
> Those who would give up essential Liberty, to purchase a little temporary
> Safety, deserve neither Liberty nor Safety.
> -- Benjamin Franklin
> "carpe diem quam minimum credula postero"
>
>
>
>
> 2010/12/16 Виноградов Юрий <vin123...@mail.ru>:
>> I am using tcprewrite version 3.4.1 (build 2229).
>>
>> -----Original Message-----
>> From: Aaron Turner [mailto:synfina...@gmail.com]
>> Sent: Thursday, December 16, 2010 12:42 AM
>> To: Main forum for tcpreplay
>> Subject: Re: [Tcpreplay-users] tcprewrite: UDP checksum error when
>> fragmenting it
>>
>> 2010/12/15 Виноградов Юрий <vin123...@mail.ru>:
>>> Hello everyone!
>>>
>>>
>>>
>>> I have an error in checksum field in first UDP-fragment, when I try to make
>>> fragmentation my one UDP datagram.
>>>
>>> As I know, the checksum original UDP datagram must be the same as checksum
>>> fragmented UDP datagram, but I get different L
>>>
>>> my script is:
>>>
>>> tcprewrite --fragroute=frag.cfg --infile=1udp.pcap --outfile=1udp_frag.pcap
>>>
>>> my frag.cfg contains:
>>>
>>> ip_frag 1000
>>>
>>> 1udp.pcap is ~1300 bytes long
>>
>> Possible bug. what version of tcprewrite are you using?
>>
>
--
Aaron Turner
http://synfin.net/ Twitter: @synfinatic
http://tcpreplay.synfin.net/ - Pcap editing and replay tools for Unix & Windows
Those who would give up essential Liberty, to purchase a little temporary
Safety, deserve neither Liberty nor Safety.
-- Benjamin Franklin
"carpe diem quam minimum credula postero"
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