[dpdk-dev] Unable to change source MAC address of packet

[Lu, Wenzhuo]

Hi Padam,

> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Padam Jeet Singh
> Sent: Thursday, October 27, 2016 10:45 PM
> To: Wiles, Keith
> Cc: dev at dpdk.org
> Subject: Re: [dpdk-dev] Unable to change source MAC address of packet
> 
> 
> > On 27-Oct-2016, at 7:37 pm, Wiles, Keith <keith.wiles at intel.com> wrote:
> >
> >
> >> On Oct 27, 2016, at 6:33 AM, Padam Jeet Singh <padam.singh at inventum.net>
> wrote:
> >>
> >> Hi,
> >>
> >> I am crafting a packet in which the source MAC address as set in the Ethernet
> header is different than the transmit port’s default MAC address. A packet
> capture of the packets coming out of this port however comes with source MAC
> address of the port’s default MAC address.
> >>
> >> Altering the destination MAC address works fine and shows up correctly in
> packet capture.
> >>
> >> The underlying network interface is an i210 and some logs added to the
> eth_igb_xmit_pkts function show that the packets I have crafted indeed are
> reaching the driver with the source MAC address set in the packet code of the
> application.
> >>
> >> How can I disable this automatic source MAC address setting?
> >
> > The packets sent with rte_eth_tx_burst() are not forced to a give MAC address.
> If you are using something on top of DPDK like Pktgen or OVS or something,
> then it may try to force a source MAC address.
> 
> No… not using pktgen or OVS. Plain simple code to take a packets from a KNI,
> change source mac address on all received packets,  and then tx_burst them to a
> port.
> 
> > Maybe the hardware does it, but we need to know the NIC being used and
> then someone maybe able to answer. I do not know of any Intel NICs do that.
> 
> Intel i210 NIC (gigabit Ethernet) is being used. I have gone through the i210
> documentation and can’t see anything specific to setting of MAC address in
> hardware for TX side. For RX side there are validations like MAC filtering, but
> nothing over TX.
> 
> >
> > Is this what you are doing.
> 
> I agree that rte_eth_tx_burst does not overwrite the source MAC as I was able
> to trace all the way to the IGB driver that source mac makes it intact. There is no
> offload flags enabled in the mbuf. Yet the packets to the other side comes out
> as with source mac address of the port.
> 
> Is there any standard DPDK app which crafts packets with different source MAC
> than the port’s physical mac? (I checked the l2fwd example loads the port mac
> before transmitting and then uses the same in TX function).
I don’t have a i210 on hand, so I checked the datasheet of i210. I don't find any description about HW will change the MAC address in the frame. I believe HW should send the frame provided by SW except doing some offload like checksum...
May I suggest to use testpmd forwarding a packet which has a different src MAC than the port's?

> 
> >
> >>
> >> Thanks,
> >> Padam
> >
> > Regards,
> > Keith
> >