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Thread: KVM/QEMU bridged mode Packets not getting to guest

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  1. #1
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    KVM/QEMU bridged mode Packets not getting to guest

    Hi All,

    This question, and a lot more detail, is also over on askubuntu.com. I know several users from here also frequent askubuntu.com, but for those that don't...

    I prefer to run my VM's on my LAN, and therefore want to to use bridged mode. I have never been able to make this work properly on my 20.04 Ubuntu test server. It works fine on my systemd/networkd Debian server and used to work fine on pre-netplan (pre systemd/networkd) Ubuntu servers.

    Packets that should be sent onwards to the vnet NICs are not. They don't even appear on tcpdump on the host bridge. The packets just seem to get dropped from the link layer. The behaviour seems much like non-promiscuous mode, but I have done specific tests ensuring everything is in promiscuous mode with the same results.

    I never run containers (lxc, lxd, docker) and do not have the br_netfilter module loaded, nor any iptables rules at all, and I want it that way.

    I have tried pretty much everything from every reference I have found.
    Any follow-up information on your issue would be appreciated. Please have the courtesy to report back.

  2. #2
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    Re: KVM/QEMU bridged mode Packets not getting to guest

    At this point, I have tossed netplan and trying via systemd-networkd directly.
    This issue has been driving me crazy for some time now.
    Any follow-up information on your issue would be appreciated. Please have the courtesy to report back.

  3. #3
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    Re: KVM/QEMU bridged mode Packets not getting to guest

    For my 20.04 test server host, the up to date kernel is:

    5.4.0.72 , as I do not run HWE.

    That kernel and various predecessors that I still have installed do not work for this application.
    The next Development kernel I still have installed, is 5.8.0, and it works fine for this application, as does any others I have installed and tried up to and including 5.12-rc6.

    While I pretty much never run the stock kernel, I was doing so for this work on purpose and out of caution. I so wish I had tried another kernel weeks ago.
    Any follow-up information on your issue would be appreciated. Please have the courtesy to report back.

  4. #4
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    Re: KVM/QEMU bridged mode Packets not getting to guest

    So - no chance of posting the working netplan.yaml file?
    This is on of the last reasons I haven't moved our VM servers to 20.04.

  5. #5
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    Re: KVM/QEMU bridged mode Packets not getting to guest

    Quote Originally Posted by TheFu View Post
    So - no chance of posting the working netplan.yaml file?
    This is on of the last reasons I haven't moved our VM servers to 20.04.
    It is also the reason I waited so long to move away from my 16.04 servers and the reason my main server is now Debian. I actually think my yaml file posted over on ask might work, but not sure if I re-install netplan to see. I actually prefer to use systemd-networkd directly. It is late in my time zone, I'll pick this up in the morning.

    EDIT: Bear with me, TheFu. I am pretty dense at times. It turns out my hardware is too new to be running 20.04 without the HWE stack, but I only figured that out about 3/4 of the way through bisecting the kernel in an attempt to determine what needed to be backported to the kernel 5.4 series. I moved my NVME drive from my previous test server to my new one, but didn't think about perhaps needing the HWE stack. Well, I paid a big price in terms of wasted time. However, I can not install the HWE stuff, because I have un-installed netplan, upon which it depends. So, I need some time to roll back some of my changes, re-install netplan and re-test to be sure. Then I'll come back here and post what I did. Eventually I will delete my question over on askubuntu (no need to advertise my stupidity).
    Last edited by Doug S; May 8th, 2021 at 10:00 PM.
    Any follow-up information on your issue would be appreciated. Please have the courtesy to report back.

  6. #6
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    Re: KVM/QEMU bridged mode Packets not getting to guest

    If I don't do something dumb at least once a day, I start to worry.
    When I hit 10x in 1 day, it is time for a beer and sleep.

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