On Thu, 18 Feb 2021 07:18:44 -0700
Gabe Stanton via Dng <dng@???> wrote:

> I'm sorry for the confusion. That was not the guide I used. I did find
> the guide I used. It seems pretty straight forward, and I believe it
> clears up all the confusion and questions caused by my previous email.
>
> https://www.debian.org/doc/manuals/debian-handbook/sect.virtualization.en.html#sect.lxc.network

Thanks Gabe. The preceding link helped, but was not sufficient.
Although better than most, it shares the same ambiguities as the
others, including not telling whether they're referring to the metal
host or the VM guest when discussing TAPs, bridges, devices and the
like. Also, like most of the others, they don't specifically identify
what should go in the "id=" slots.

Based on the preceding link, I deduce that the TAP is created by the
guest VM, in such a way that it attaches to the bridge created on the
metal host, and therefore I have no need to create a TAP on the metal
host.

Here's my progress so far, based on the link you supply above and my
other readings and experimentation:

***

I build the bridge purely with ip commands. Also, I don't mess
with the firewall (which perhaps has been my problem all along). I'll
investigate this tomorrow.

Below are some scripts and stuff I'm using. The following is
upnet.sh, which I use to set up networking on the metal host, which
happens to run Void Linux, which has no /etc/network/interfaces:

=========================================
#!/bin/sh

use_bridge=1
use_tap=0

dev="enp40s0"
ipaddr_major="192.168.0.2"
ipaddr_minor="192.168.0.102"
gateway="192.168.0.1"

error_tap_without_bridge(){
echo -n "ERROR: Can\'t set TAP without "
echo -n "BRIDGE! "
echo Aborting...
exit 1
}


enable_ip_forwarding(){
echo 1 > /proc/sys/net/ipv4/ip_forward
}

unset_everything(){
dev=$1
ip_maj=$2
ip_min=$3
gateway=$4
echo "Unsetting everything for $dev, $ip_maj and $ip_min"
ip link set dev tap0 down
brctl delif br0 tap0
ip link del tap0
ip link set dev br0 down
ip addr del $ip_min/24 dev br0
ip addr del $ip_maj/24 dev br0
brctl delbr br0
ip link set dev $dev down
ip addr del $ip_min/24 dev $dev
ip addr del $ip_maj/24 dev $dev
echo ""
}

set_hostname_and_localhost(){
echo "Setting hostname and localhost"
hostname=`grep -v "^\s*#" /etc/hostname | head -n1`
ip link set dev lo up
echo ""
}

create_phys_device_link(){
dev=$1
echo Creating device link for $dev
ip link set dev $dev up
echo ""
}

set_phys_device_addr(){
dev=$1
ip_maj=$2
ip_min=$3
gateway=$4
echo -n "Setting physical device addresses "
echo -n "$ip_maj "
echo -n "and $ip_min "
echo -n "for $physdev "
echo "with gateway $gateway"
ip link set dev $dev down
ip addr add $ip_maj/24 dev $dev
ip addr add $ip_min/24 dev $dev
ip link set dev $dev up
ip route add default via $gateway
echo ""
}

set_bridge(){
dev=$1
ip_maj=$2
ip_min=$3
gateway=$4
echo Setting bridge for $dev
echo -n "Creating and setting bridge addresses "
echo -n "$ip_maj "
echo -n "and $ip_min "
echo -n "for $physdev "
echo "with gateway $gateway"

ip link add name br0 type bridge
ip link set dev $dev master br0
ip addr add $ip_maj/24 dev br0
ip addr add $ip_min/24 dev br0
ip link set dev br0 up
ip route add default via $gateway
echo ""
}

set_tap(){
echo Setting tap
ip tuntap add tap0 mode tap
brctl addif br0 tap0
#ip addr add 192.168.0.66/24 dev tap0
ip link set dev tap0 up
echo ""
}

show_networking(){
echo -n "Networking follows in 3 seconds..."
sleep 3
echo "\n"
echo "========================================"
echo "========================================"
ip -4 link
echo "......................"
ip -4 addr
echo "......................"
ip -4 route
echo "========================================"
echo "========================================"
}

echo "\nBegin upnet.sh"

[ "$use_tap" = "1" ] && [ "$use_bridge" != "1" ] && \
error_tap_without_bridge

unset_everything $dev $ipaddr_major $ipaddr_minor $gateway

enable_ip_forwarding

set_hostname_and_localhost

create_phys_device_link $dev $ipaddr_major $ipaddr_minor $gateway

[ "$use_bridge" = "1" ] || \
set_phys_device_addr $dev $ipaddr_major $ipaddr_minor $gateway

[ "$use_bridge" = "1" ] && set_bridge $dev \
$ipaddr_major $ipaddr_minor $gateway

[ "$use_tap" = "1" ] && \
set_tap $dev $ipaddr_major $ipaddr_minor $gateway

show_networking
=========================================

The preceding just builds br0 with ip addresses 192.168.0.2 and
192.168.0.102, default route (gateway) 192.168.0.1, for my metal host,
and runs every time my metal host is rebooted (or it can be run any
time). It has provisions to build a tap, or to not build a bridge and
instead assign the IP addresses and default route to enp40s0 itself.

The next shellscript runs on my metal host to launch a (Devuan) VM
guest:

=========================================
#!/bin/sh

dvddir=/scratch/linuxinst/devuan/devuan_beowulf/installer-iso

qemu-system-x86_64 --enable-kvm \
-cdrom $dvddir/devuan_beowulf_3.0.0_amd64-desktop.iso \
-hda /scratch/qemu_images/beowulf.disk \
-m 4G \
-boot c \
-netdev bridge,id=mybridge0,br=br0 \
-netdev user,id=mynet0,restrict=no,net=192.168.0.0/24 -device e1000,netdev=mynet0 \


=========================================

In the preceding, notice that the blank line at the end is necessary to
end the series of backslashed lines. I backslash ALL the lines so
experimentally I can move things in and out and rearrange. Like I said,
I've tried hundreds of combinations.

In the preceding, I didn't declare a TAP. As best I could read the
various conflicting documentation, the VM guest *creates* the tap and
connects it to the metal host created bridge, so no need to create the
TAP on the metal host. But then again, I've tried it both ways.

One hint I've gotten, a hint which I cannot bring to fruition because
of sparse and contradictory documentation, is that this brings up a "no
peer for mybridge0" warning. I've tried substituting both "eth0",
enp40s0, and "junk" for "mybridge0", and as I remember (hundreds of
experiments, didn't write them all down), doing so didn't affect the
symptom (the no peer warning). I chose the preceding script due to the
following documentation, which seemed better than most:

https://www.debian.org/doc/manuals/debian-handbook/sect.virtualization.en.html#sect.lxc.network

On my Devuan *guest* VM, I have the following /etc/network/interfaces,
as suggested by a careful reading of
https://www.debian.org/doc/manuals/debian-handbook/sect.virtualization.en.html#sect.lxc.network

=========================================
source /etc/network/interfaces.d

auto lo
iface lo inet loopback

auto eth0
allow-hotplug eth0

auto tap0
iface tap0 ifacem manual
vde-switch -t tap0

auto br0 inet static
bridge-ports tap0
address 192.168.0.60
netmask 255.255.255.0
=========================================

When, on the *host*, I run my instantiations script to create a guest
VM, the following is output to the terminal:

=========================================
[root@mydesk qemu_images]# ./runbeowulf.sh
WARNING: Image format was not specified for
'/scratch/qemu_images/beowulf.disk' and probing guessed raw.
Automatically detecting the format is dangerous for raw images, write
operations on block 0 will be restricted. Specify the 'raw' format
explicitly to remove the restrictions. qemu-system-x86_64: warning:
netdev mybridge0 has no peer
=========================================

After that, my Devuan guest VM appears, to which I log in and run a
terminal. IP addresses are 192.168.0.15 for the guest VM itself, and
192.168.0.2 (my metal host) for the default route.

The VM guest can lynx to my nginx server on 192.168.0.2, and to any
HTML page on the Internet, but cannot lynx to my printer at
192.168.0.13 and my metal cable modem at 192.168.0.1. From my metal
desktop (which runs the guest VM) at 192.168.0.2 I cannot ssh to
slitt@192.168.0.15:

=========================================
[slitt@mydesk qemu]$ ssh slitt@192.168.0.15
ssh: connect to host 192.168.0.15 port 22: No route to host
[slitt@mydesk qemu]$
=========================================

I'm pretty sure "no route to host" means this isn't caused by a
firewall problem, although once I fix the routing thing, that might
unmask a further firewall problem.

In other words, my VM guest is in no way a peer of the various metal
hosts on my 192.168.0.0/24 physical Ethernet network.

If anybody has any words of wisdom, and can identify whether each
wisdom word applies to the metal host or the guest VM, I'd love to hear
them.

Thanks,

SteveT

Steve Litt
Autumn 2020 featured book: Thriving in Tough Times
http://www.troubleshooters.com/thrive