Hi Vladim. Thanks a lot for your reply.
Looking at the example packet you sent, I made a change into my config file. I changed the MAC destination address to 0xFF .... 0xFF (broadcast). Then, I receive the packet successfully thru the loopback interface. Same thing if I use 0x00...0x00 instead of 0xFF....0xFF. Thanks a lot for all your help and regards. -Bob El miércoles, 2 de noviembre de 2016, 6:36:29 (UTC+1), Vadim Kochan escribió: > > On Thu, Oct 27, 2016 at 11:49 AM, <roberto....@bitmonlab.com > <javascript:>> 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 > >> > >> > > >> > >> > -- > >> > >> > You received this message because you are subscribed to the Google > Groups "netsniff-ng" group. > >> > >> > To unsubscribe from this group and stop receiving emails from it, > send an email to netsniff-ng...@googlegroups.com. > >> > >> > For more options, visit https://groups.google.com/d/optout. > >> > >> > >> > >> 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 > > > > -- > > You received this message because you are subscribed to the Google > Groups "netsniff-ng" group. > > To unsubscribe from this group and stop receiving emails from it, send > an email to netsniff-ng...@googlegroups.com <javascript:>. > > For more options, visit https://groups.google.com/d/optout. > > 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 > -- You received this message because you are subscribed to the Google Groups "netsniff-ng" group. To unsubscribe from this group and stop receiving emails from it, send an email to netsniff-ng+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.