[dpdk-dev] Issue with pktgen-dpdk replaying >1500bytes pcap on MCX4

[Wiles, Keith]

> On Sep 25, 2017, at 6:19 PM, Damien Clabaut <damien.clabaut at corp.ovh.com> wrote:
> 
> Hello DPDK devs,
> 
> I am sending this message here as I did not find a bugtracker on the website.
> 
> If this is the wrong place, I would kindly apologize and ask you to redirect me to the proper place,
> 
> Thank you.
> 
> Description of the issue:
> 
> I am using pktgen-dpdk to replay a pcap file containing exactly 1 packet.
> 
> The packet in question is generated using this Scapy command:
> 
> pkt=(Ether(src="ec:0d:9a:37:d1:ab",dst="7c:fe:90:31:0d:52")/Dot1Q(vlan=2)/IP(dst="192.168.0.254")/UDP(sport=1020,dport=1021)/Raw(RandBin(size=8500)))
> 
> The pcap is then replayed in pktgen-dpdk:
> 
> ./app/app/x86_64-native-linuxapp-gcc/pktgen -l 0-7 -- -m [1-7].0 -s 0:pcap/8500Bpp.pcap

This could be the issue as I can not setup your system (no cards). The pktgen command line is using 1-7 cores for TX/RX of packets. This means to pktgen to send the pcap from each core and this means the packet will be sent from each core. If you set the number of TX/RX cores to 1.0 then you should only see one. I assume you are using 1-7 cores to increase the bit rate closer to the performance of the card.

> 
> When I run this on a machine with Mellanox ConnectX-4 NIC (MCX4), the switch towards which I generate traffic gets a strange behaviour
> 
> #sh int et29/1 | i rate
>   5 seconds input rate 39.4 Gbps (98.4% with framing overhead), 0 packets/sec
> 
> A capture of this traffic (I used a monitor session to redirect all to a different port, connected to a machine on which I ran tcpdump) gives me this:
> 
> 19:04:50.210792 00:00:00:00:00:00 (oui Ethernet) > 00:00:00:00:00:00 (oui Ethernet) Null Unnumbered, ef, Flags [Poll], length 1500
> 19:04:50.210795 00:00:00:00:00:00 (oui Ethernet) > 00:00:00:00:00:00 (oui Ethernet) Null Unnumbered, ef, Flags [Poll], length 1500
> 19:04:50.210796 00:00:00:00:00:00 (oui Ethernet) > 00:00:00:00:00:00 (oui Ethernet) Null Unnumbered, ef, Flags [Poll], length 1500
> 19:04:50.210797 00:00:00:00:00:00 (oui Ethernet) > 00:00:00:00:00:00 (oui Ethernet) Null Unnumbered, ef, Flags [Poll], length 1500
> 19:04:50.210799 00:00:00:00:00:00 (oui Ethernet) > 00:00:00:00:00:00 (oui Ethernet) Null Unnumbered, ef, Flags [Poll], length 1500
> 
> The issue cannot be reproduced if any of the following conditions is met:
> 
> - Set the size in the Raw(RandBin()) to a value lower than 1500
> 
> - Send the packet from a Mellanox ConnectX-3 (MCX3) NIC (both machines are indentical in terms of software).
> 
> Is this a known problem ?
> 
> I remain available for any question you may have.
> 
> Regards,
> 
> -- 
> Damien Clabaut
> R&D vRouter
> ovh.qc.ca
> 

Regards,
Keith