On Thu, Oct 27, 2016 at 11:49 AM, <roberto.vaquer...@bitmonlab.com> wrote:
> El miércoles, 19 de octubre de 2016, 17:23:40 (UTC+2), emacsu...@gmail.com
> escribió:
>> El miércoles, 19 de octubre de 2016, 12:46:45 (UTC+2), Vadim Kochan
>> escribió:On Wed, Oct 19, 2016 at 1:38 PM, <emacsu...@gmail.com> wrote:
>>
>> > Hello.
>>
>> >
>>
>> > I'm having a problem when trying to send packets with trafgen to the
>> > loopback interface.
>>
>> >
>>
>> > Packets sent this way do not reach their destination.
>>
>> >
>>
>> > However, if packets are sent from an external machine, then I have no
>> > problem at all to receive these packets at the destination application.
>>
>> >
>>
>> > I use "-o lo" option on the command line when executing trafgen.
>>
>> >
>>
>> > I suspect the problem is that I'm building an incorrect packet, and the
>> > kernel is discarding it.
>>
>> >
>>
>> > The ethernet header on my cfg file looks like the following:
>>
>> >
>>
>> > --------------------------------------
>>
>> > #include <stddef.h>
>>
>> >
>>
>> > {
>>
>> > fill(0x00, ETH_ALEN),
>>
>> > fill(0x00, ETH_ALEN),
>>
>> > c16(ETH_P_LOOP),
>>
>> > c32(0x00),
>>
>> >
>>
>> > ......
>>
>> >
>>
>> > (Both source and destination IP addresses are set to 127.0.0.1)
>>
>> > --------------------------------------
>>
>> >
>>
>> > I have tried other combinations, like removing the ethernet header
>> > completely, for instance.
>>
>> >
>>
>> > None of them worked.
>>
>> >
>>
>> > How does the ethernet header have to to look like, when you want trafgen
>> > to generate a valid packet to be sent thru the loopback interface?
>>
>> >
>>
>> > Thanks a lot.
>>
>> > -Bob
>>
>> >
>>
>> > --
>>
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>>
>>
>>
>> Hi Bob,
>>
>>
>>
>> Does it work if to increase packet length to 64 bytes length ?
>>
>>
>>
>> Sorry, I have no time to check it right now, will do it later if the
>>
>> above's approach did not help.
>>
>>
>>
>> Regards,
>>
>> Vadim Kochan
>>
>>
>>
>>
>>
>>
>> Hi Vadim.
>>
>>
>> Thanks for the prompt response.
>>
>>
>> So far, I have been using the ETH_P_LOOP value (96), to indicate that the
>> packet corresponds to a loopback packet.
>> Given that that field is used for both type and length, if I'm understanding
>> you correctly, you want me to change it to a value indicating the length of
>> my entire packet, and not the value of ETH_P_LOOP.
>> I suppose you said 64 as an example, and the value there should in fact
>> correspond to my actual packet length.
>>
>>
>> I have followed this approach, but the packet does not reach my application,
>> still.
>>
>>
>> In fact, on second thoughts, I cannot see the point on using ETH_P_LOOP
>> value at all in the ethernet header, since its value is 96, which means that
>> we have to interpret that value as a length, but the packet length can be
>> anything.
>>
>>
>> Not sure if I'm missing something here ....
>>
>>
>> Any idea?
>>
>>
>> Thanks.
>> -Bob
>>
>>
>>
>>
>>
>>
>>
>
>
> Hello.
>
> Any idea on why I'm not able to make traffic get to its destination thru the
> loopback interface?
>
> Not sure if the problem is the ethernet header I'm using. I guess so, but I
> have tried all combinations with no success.
>
> Thanks.
> -Bob
>
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Sorry for such a delay, I am very busy with my regular job ...
But do you have an issue with sniffing such loopback packet ?
For example I tried the following trafgen packet and I did receive it
via w-shark:
$ sudo trafgen/trafgen --dev lo '{ fill(0xff, 6), 0x00, 0x02, 0xb3,
rnd(3), c16(0x0060), fill(0xca, 64) }' -n 1
$ uname -a
Linux angus-think 4.7.2-1-ARCH #1 SMP PREEMPT Sat Aug 20 23:02:56 CEST
2016 x86_64 GNU/Linux
And BTW, EtherType values of 1500 and below for this field indicate
that the field is used as the size of the payload of the Ethernet
frame while values of 1536 and above indicate that the field is used
to represent EtherType.
And w-shark shows it as LLC packet.
Regards,
Vadim Kochan
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