From mboxrd@z Thu Jan  1 00:00:00 1970
From: Liran Alon <liran.alon@oracle.com>
Subject: Re: Networking Problems with Debian Stretch + KVM + old Linux Guest
Date: Sat, 20 Jan 2018 12:57:28 -0800 (PST)
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To: <hermann@qwer.tk>
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----- hermann@qwer.tk wrote:

> Hi,
> I today upgraded my KVM host from Debian 8 to the latest Debian 9
> (Stretch). This worked perfectly, however, 2 old guest systems (SuSE
> 9.1, kernel 2.6.7 / 2.6.5) have no network access.
>=20
> All other machines running on this host are Linux Debian machines and
> use the "virtio" networking drivere whereas those two old machines
> use
> RTL8139 (or e1000, makes no difference).
>=20
> On the guest side, the networking interface (eth0 / rtl8139) is up,
> it
> states "Link Up / 100MBit" in the log file, everything looks fine, but
> I
> can't get out, no ping, empty arp table etc.
>=20
> Basically, I use bridging for the virtual hosts, this looks like
> this:
>=20
> br0             8000.0026186273f4       no              eth0
>                                                         vnet0
>                                                         vnet1
>=20
> or like so:
>=20
> port no mac addr                is local?       ageing timer
>   1     00:00:24:cc:c7:85       no                 0.42
>   1     00:19:66:b3:cb:34       no                 3.97
>   1     00:22:b0:cf:04:b2       no                 0.03
>=20
>=20
> What is interesting is that I cannot find the MAC Address of the 2
> machines in the above table, which is probably not good.
>=20
> Forwarding is enabled for all bridges and there is no packet filter /
> firewall.
>=20
> I have no clue how to solve this problem - do you have any idea?
>=20
> Kernel version (uname -rv):
> Linux version 4.9.0-5-amd64 (debian-kernel@lists.debian.org) (gcc
> version 6.3.0 20170516 (Debian 6.3.0-18) ) #1 SMP Debian
> 4.9.65-3+deb9u2
> (2018-01-04)
>=20
> kvm --version:
> QEMU emulator version 2.8.1(Debian 1:2.8+dfsg-6+deb9u3)
>=20
>=20
> Best Regards,
> Hermann
>=20
> --=20
> hermann@qwer.tk
> PGP/GPG: 299893C7 (on keyservers)

1. What do you see when sniffing (with tcpdump) the QEMU's tap devices whic=
h represent the guest's NICs? Do you see any traffic there?

2. Examining the KVM events trace may also be helpful. It's very easy to ex=
tract:
# echo 1 >/sys/kernel/debug/tracing/events/kvm/enable
# cat /sys/kernel/debug/tracing/trace_pipe > /tmp/trace
# echo 0 >/sys/kernel/debug/tracing/events/kvm/enable

Regards,
-Liran