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[Qemu-discuss] Query regarding transparent passing of L2 headers with QE
Ramadoss, Kumar 1. (Nokia - IN/Chennai)
[Qemu-discuss] Query regarding transparent passing of L2 headers with QEMU sessions
Tue, 26 Mar 2019 04:55:16 +0000
This query is regarding transparent passing of L2 headers with QEMU session. I
have started a QEMU session from my Centos Linux to start a virtual machine.
Guest environment is started and running. Typically, QEMU creates a tap
interface (say tap0) in the Centos Linux for which there would be a
corresponding interface in the guest environment (say eth0). If I am sending
packet from say a traffic generator to tap0, then this packet would be
available at eth0 also in the guest environment for processing.
Problem which I am facing is that if I am sending a packet with a VLAN tag
[meaning with dst mac, src mac, VLAN tag [priority bits + VLAN] + IP headers on
top of that], this packet is received as it is in the eth0 interface (in guest
environment), but the only difference which i see is that if the priority bits
is set to some (other than 0), then when it is received on the eth0 interface
it is still received with priority bit as 0. But the VLAN is received as it was
sent from the traffic generator.
I want to know whether QEMU is doing something that this priority bits is
getting lost (filled with 0. Or is it some settings requried in QEMU for this
be received transparently in eth0 interface in the guest environment? Or is
this has nothing to do with QEMU?
Because, I tried the same without any QEMU by just have veth pairs and sent the
packet from the generator to one interface in the pair, priority bits are
received on the other interface in the pair as it is.
Is this a known bug in QEMU? B'cos I tried this with Ubuntu linux distribution
as the VM and I still see that the priority bits are not passed transparently
to the guest.
For eg. Following was the command used with QEMU for starting ubuntu:
/bin/qemu-system-x86_64 -m 2048 -boot d -enable-kvm -smp 3 -netdev
e1000,netdev=network1,mac=00:00:00:01:0C:77 -hda testing-image.img -cdrom
It would be helpful, if some insight is provided for the above query.
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