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Re: [Xen-users] all packets between certain guests on the same host being dropped

On 01/11/2017 09:47 AM, WebDawg wrote:

On Tue, Jan 10, 2017 at 2:19 PM, Sherrard Burton <sburton@xxxxxxxxxxxxx
<mailto:sburton@xxxxxxxxxxxxx>> wrote:

    all packets are being dropped in a debian 7 (wheezy) guest only when
    they are coming from a debian 5 (lenny) guest on the same host. the
    console and kernel log report  'net eth0: Invalid extra type: 4'
    when packets are being dropped. the problem goes away if i change
    wheezy configuration from 1 vcpu to >1 vcpu. i tested all of this on
    fresh, minimal installs, so AFAICT there are no firewalls or other
    esoteric settings involved.

    this is a strange one, so please forgive me if i omit some useful

    i have a pair of xen hosts which are running pairs of guest HA
    pairs. for example:



    with various HA solutions implemented within the guests. this is not
    germane to the particular problem, but germane to how i discovered
    it. for the sake of balancing, i have configured the guests' HA
    preferences so that the active nodes tend to be on different hosts.
    so under normal circumstances, apache-guest1 and haproxy-guest2
    would be the active nodes. no problem at all in that situation.

    but i discovered that i cannot communicate between apache-guest1 and
    haproxy-guest1, located on the same host. after much tcpdumping in
    the host and guests, i discovered that the problem is unidirectional
    and specific to a particular OS combination.

    a) inbound packets to a debian wheezy guest are dropped only when
    they originate from a debian lenny guest on the same host

    b) outbound packets from a wheezy guest to a lenny guest are passed
    correctly, even though the wheezy cannot see the return
    communication from the lenny guest

    c) there is no problem communicating to or from the wheezy guest and
    an identically-configured lenny guest on the other host

    d) there is no problem communicating to or from other combinations
    of guests on the same host. ie, from jessie to wheezy, lenny to
    lenny and wheezy to wheezy, etc.

    even stranger, my attempts in trying to narrow it down to the
    simplest possible test case led me to discover that for the same
    exact guest, changing the vcpu setting from 1 to >1 makes the
    problem go away.

    sburton@host:~$ virsh -c xen:/// dumpxml wheezy-guest >
    # test and reconfigure
    sburton@host:~$ virsh -c xen:/// dumpxml wheezy-guest > ~/can-ping.xml

    sburton@host:~$ diff ~/can-ping.xml ~/cannot-ping.xml
    <   <vcpu placement='static'>2</vcpu>
    >   <vcpu placement='static'>1</vcpu>

    testing methodology:
    simple ping between hosts.

    initially broken because the ARP 'is-at' traffic from the lenny
    guest is dropped going into the wheezy guest, and ARP 'who-has'
    traffic from the lenny guest is dropped going into the wheezy guest.
    therefore the guests cannot discover one another.

    after manually setting the ARP cache entries on both guests:

    pinging from lenny to wheezy, tcpdump shows ICMP echo requests in
    the lenny guest and on the VIFs for both guests in the host. but the
    ICMP requests are unseen in the wheezy guest.

    pinging from wheezy to lenny, tcpdump shows ICMP echo requests and
    replies in the lenny guest and on the VIFs for both guests in the
    host. ICMP requests are seen in the wheezy guest, since they
    originate there, but the replies from the lenny guest are unseen.

    the problem is not limited to ARP or ICMP, all other communication i
    have tried fails similarly.

    the smoking gun (i hope):
    when packets are being dropped in the wheezy guest, the console and
    various logs report
    [ 6977.669408] net eth0: Invalid extra type: 4

    and the only reference i have found via my searching is this thread:

    which seems to be unresolved.

    i'm hoping that some part of this tickles someone's memory, or
    piques their interest, or at least that someone can point me to some
    more troubleshooting steps i haven't thought of.


    setup details:
    sburton@host:~$ cat /etc/issue
    Debian GNU/Linux 8 \n \l

    sburton@host:~$ uname -a
    Linux host 4.7.0-0.bpo.1-amd64 #1 SMP Debian 4.7.8-1~bpo8+1
    (2016-10-19) x86_64 GNU/Linux

    sburton@host:~$ dpkg -l | grep -F -e libvirt-daemon -e
    xen-hypervisor -e qemu-system
    ii  libvirt-daemon                  1.2.9-9+deb8u3
     amd64      programs for the libvirt library
    ii  libvirt-daemon-system           1.2.9-9+deb8u3
     amd64      Libvirt daemon configuration files
    ii  qemu-system-common              1:2.7+dfsg-3~bpo8+2
    amd64      QEMU full system emulation binaries (common files)
    ii  qemu-system-x86                 1:2.7+dfsg-3~bpo8+2
    amd64      QEMU full system emulation binaries (x86)
    ii  xen-hypervisor-4.4-amd64        4.4.1-9+deb8u8
     amd64      Xen Hypervisor on AMD64

    sburton@host:~$ grep -F -A1 '<os>' ~/cannot-ping.xml
        <type arch='x86_64' machine='xenfv'>hvm</type>

    sburton@host:~$ grep -F -C2 'xenbr0' ~/cannot-ping.xml
        <interface type='bridge'>
          <mac address='00:16:3e:fb:2e:1c'/>
          <source bridge='xenbr0'/>
          <model type='rtl8139'/>

    sburton@host:~$ ip addr show xenbr0
    8: xenbr0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue
    state UP group default qlen 1000
        link/ether bc:30:5b:f0:32:b4 brd ff:ff:ff:ff:ff:ff
        inet <> brd scope global xenbr0
           valid_lft forever preferred_lft forever
        inet6 fe80::be30:5bff:fef0:32b4/64 scope link
           valid_lft forever preferred_lft forever

    fullvirt installs, created from netinst ISO via virt-manager running
    on my workstation, manipulated through some combination of
    virt-manager and local virsh commands.

    root@wheezy-guest:~# uname -a
    Linux wheezy-guest 3.16.0-0.bpo.4-amd64 #1 SMP Debian
    3.16.36-1+deb8u2~bpo70+1 (2016-10-19) x86_64 GNU/Linux

    root@wheezy-guest:~# cat /etc/issue
    Debian GNU/Linux 7 \n \l

    root@lenny-guest:~# uname -a
    Linux lenny-guest 2.6.26-2-amd64 #1 SMP Sun Mar 4 21:48:06 UTC 2012
    x86_64 GNU/Linux

    root@lenny-guest:~# cat /etc/issue
    Debian GNU/Linux 5.0 \n \l

I do not know if this helps at all:

that is the tail end of the "unresolved" thread i mentioned.

i'm using the stock debian packages, and i have not poked around in the netfront driver, so i'm not intimately familiar with the suggested code changes. but i'm sure that i could insert some debugging and recompile given a little guidance.

thanks for the response.

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