Bearbeiten von „VLAN for virtual machines“

== Introduction ==
I wanted to update VLAN connections for virtual
machines to newer technologies and put a question on
[https://unix.stackexchange.com/questions/392758/setup-vlan-on-linux-bridge-for-virtual-machines-with-systemd unix.stackexchange]. But I do not get any answer. It seems there is very
little knowledge for this out there. So I decided to work on it by myself
and document it here.

In gerneral I will look at three methods:
# [[#oldstyle linux bridge as hub|oldstyle linux bridge as hub]]
# [[#linux bridge as hub|linux bridge as hub]]
# [[#linux bridge with libvirt hook scripts|linux bridge with libvirt hook scripts]]

== Preparation ==
I have Debian GNU/Linux 9.1 (stretch) on the host and on virtual machines for testing. Setup is described here: [[Setup KVM with console]]. I'm sitting on harley as host, my all day workstation.
Now I start the virtual machine, login and show its interface setting:
 '''harley$''' virsh start --console deb9-test
login
 '''deb9-test$''' cat /etc/systemd/network/08-vlan10.netdev
 [NetDev]
 Name=vlan10
 Kind=vlan
 [VLAN]
 Id=10
 '''deb9-test$''' cat /etc/systemd/network/12-vlan10_attach-to-if.network
 [Match]
 Name=ens2
 [Network]
 VLAN=vlan10
 '''deb9-test$''' cat /etc/systemd/network/16-vlan10_up.network
 [Match]
 Name=vlan10
 [Network]
 DHCP=ipv4
 IPv6AcceptRA=no
 LinkLocalAddressing=no
To test if the virtual machine has connection I use:
 '''deb9-test$''' journalctl -b --no-hostname -u systemd-networkd.service
 -- Logs begin at Fri 2017-09-15 17:09:51 CEST, end at Sat 2017-09-23 20:34:20 CEST. --
 Sep 23 20:34:05 systemd-networkd[204]: Enumeration completed
 Sep 23 20:34:05 systemd[1]: Started Network Service.
 Sep 23 20:34:05 systemd-networkd[204]: vlan10: netdev ready
 Sep 23 20:34:05 systemd-networkd[204]: ens2: IPv6 enabled for interface: Success
 Sep 23 20:34:05 systemd-networkd[204]: ens2: Gained carrier
 Sep 23 20:34:05 systemd-networkd[204]: vlan10: Gained carrier
 Sep 23 20:34:06 systemd-networkd[204]: ens2: Gained IPv6LL
 Sep 23 20:34:06 systemd-networkd[204]: vlan10: Gained IPv6LL
 Sep 23 20:34:09 systemd-networkd[204]: vlan10: DHCPv4 address 192.168.10.89/24 via 192.168.10.1
 Sep 23 20:34:09 systemd-networkd[204]: vlan10: Configured
 Sep 23 20:34:19 systemd-networkd[204]: ens2: Configured
 '''deb9-test$'''
4 sec after Started Network Service it gets an IP-Address and 14 sec later interface ens2 was Configured. If ens2 is Configured and the guest hasn't got an IP-Address the connection failed. It looks like this:
 '''deb9-test$''' journalctl -b --no-hostname -u systemd-networkd.service
 -- Logs begin at Fri 2017-09-15 17:09:51 CEST, end at Sat 2017-09-23 20:45:13 CEST. --
 Sep 23 20:44:59 systemd-networkd[197]: Enumeration completed
 Sep 23 20:44:59 systemd[1]: Started Network Service.
 Sep 23 20:44:59 systemd-networkd[197]: vlan10: netdev ready
 Sep 23 20:44:59 systemd-networkd[197]: ens2: IPv6 enabled for interface: Success
 Sep 23 20:44:59 systemd-networkd[197]: ens2: Gained carrier
 Sep 23 20:44:59 systemd-networkd[197]: vlan10: Gained carrier
 Sep 23 20:45:00 systemd-networkd[197]: ens2: Gained IPv6LL
 Sep 23 20:45:00 systemd-networkd[197]: vlan10: Gained IPv6LL
 Sep 23 20:45:13 systemd-networkd[197]: ens2: Configured
 '''deb9-test$'''

Because I have to start the test virtual machine many times I setup autologin. It's no problem. There is nothing on the guest.
 '''deb9-test$''' grep ^ExecStart= /lib/systemd/system/serial-getty@.service
 ExecStart=-/sbin/agetty --keep-baud 115200,38400,9600 %I $TERM
modify to
 ExecStart=-/sbin/agetty --autologin ''yourloginname'' --keep-baud 115200,38400,9600 %I $TERM
<span id="bridge-settings">To list all settings of the bridge</span> you can use:
 '''harley$''' find /sys/class/net/br0/bridge/ -type f -readable -printf '%f = ' -exec cat {} \; | sort

== oldstyle linux bridge as hub ==
This works always with the old linux bridge that do not know anything about VLAN. The trick is to set it to a complete transparent state for all connected interfaces like a hub. But you have to know that the bridge will then forward all packets to all interfaces simultanously. You can do it by setting the ageing time to 0.

Disable systemd-networkd and start networking with ifupdown:
 '''harley$''' sudo systemctl stop systemd-networkd
 Warning: Stopping systemd-networkd.service, but it can still be activated by:
   systemd-networkd.socket
 '''harley$''' sudo systemctl disable systemd-networkd
 Removed /etc/systemd/system/multi-user.target.wants/systemd-networkd.service.
 Removed /etc/systemd/system/sockets.target.wants/systemd-networkd.socket.
 '''harley$''' sudo ip link set dev br0 down && sudo ip link del dev br0
 '''harley$''' sudo systemctl enable networking.service
 Synchronizing state of networking.service with SysV service script with /lib/systemd/systemd-sysv-install.
 Executing: /lib/systemd/systemd-sysv-install enable networking
 '''harley$''' sudo systemctl start networking.service
 '''harley$'''
Setup the bridge and start it:
 '''harley$''' cat /etc/network/interfaces
 auto br0
 iface br0 inet manual
     bridge_ports enp1s0
     bridge_ageing 0
     bridge_stp off
 '''harley$''' sudo ifup br0
 Waiting for br0 to get ready (MAXWAIT is 32 seconds).
 '''harley$'''
It's all in place now:
 '''harley$''' cat /sys/class/net/br0/bridge/ageing_time 
 0
 '''harley$''' cat /sys/class/net/br0/bridge/stp_state 
 0
 '''harley$''' cat /sys/class/net/br0/bridge/vlan_filtering 
 0
Yes, there is no VLAN filtering, means VLAN on the bridge is disabled but the guest sees the VLAN-tagged packets.

=== References ===
* https://wiki.debian.org/NetworkConfiguration#Bridging_without_Switching

== linux bridge as hub ==
Now I try to setup [[#oldstyle linux bridge as hub]] just with systemd-networkd.

Disable networking with ifupdown and start systemd-networkd:
 '''harley$''' sudo systemctl stop networking.service
 '''harley$''' sudo systemctl disable networking.service
 Synchronizing state of networking.service with SysV service script with /lib/systemd/systemd-sysv-install.
 Executing: /lib/systemd/systemd-sysv-install disable networking
 '''harley$''' sudo ip link set dev br0 down && sudo ip link del dev br0
 '''harley$''' sudo systemctl enable systemd-networkd
 Created symlink /etc/systemd/system/multi-user.target.wants/systemd-networkd.service → /lib/systemd/system/systemd-networkd.service.
 Created symlink /etc/systemd/system/sockets.target.wants/systemd-networkd.socket → /lib/systemd/system/systemd-networkd.socket.
 '''harley$''' sudo systemctl start systemd-networkd
 '''harley$'''
Setup the bridge and start it:
 '''harley$''' cat /etc/systemd/network/08-br0.netdev
 [NetDev]
 Name=br0
 Kind=bridge
 [Bridge]
 AgeingTimeSec=0
 STP=false
 '''harley$''' cat /etc/systemd/network/12-br0_add-enp1s0.network
 [Match]
 Name=enp1s0
 [Network]
 Bridge=br0
 '''harley$''' cat /etc/systemd/network/16-br0_up.network 
 [Match]
 Name=br0
 '''harley$''' sudo ip link set dev br0 down && sudo ip link del dev br0
 '''harley$''' sudo systemctl restart systemd-networkd
 '''harley$'''

AgeingTimeSec=0 is not acepted but should:
 '''harley$''' cat /sys/class/net/br0/bridge/ageing_time 
 30000   (means 300 sec)
 '''harley$'''
But I've found a workaround. Useing a number between '''.'''01 and '''.'''000001 (there are dots) will set ageing_time to 0.
So set AgeingTimeSec='''.'''000001 in /etc/systemd/network/08-br0.netdev. I suppose it's a bug. Then we
will get:
 '''harley$''' cat /sys/class/net/br0/bridge/ageing_time 
 0
 '''harley$''' cat /sys/class/net/br0/bridge/stp_state 
 0
 '''harley$''' cat /sys/class/net/br0/bridge/vlan_filtering 
 0
 '''harley$'''
The guest gets now an IP-Address on boot and is connected to VLAN 10.

=== Discussion ===
This works because of [[#References|three conditions]].
# ageing time is 0: ageing time specifies the number of seconds a MAC Address will be kept in the forwarding database after having a packet received from this MAC Address. Setting it to 0 means there is never a MAC Address stored in the FDB.
# unicast flood on interfaces is on: this controls whether the bridge should flood traffic for which an FDB entry is missing and the destination is unknown through this port. Defaults to on.
# spanning tree protocol (stp) is disabled: we don't have a forward_delay at startup for the learning phase of spanning tree.
I have a running and connected virtual machine:
 '''harley$''' sudo bridge vlan show
 port    vlan ids
 enp1s0   1 PVID Egress Untagged
 br0      1 PVID Egress Untagged
 vnet0    1 PVID Egress Untagged
 '''harley$''' cat /sys/class/net/br0/bridge/ageing_time
 0
 '''harley$''' cat /sys/class/net/br0/bridge/forward_delay
 1500
 '''harley$''' cat /sys/class/net/br0/bridge/stp_state
 0
Indeed we have forward_delay 1500 (means 15 sec) but it doesn't matter. stp_state is 0 (disabled), no spanning tree. Flood (means unicast flood) is on as I can see:
 '''harley$''' sudo bridge -d link show
 ''3: enp1s0'' state UP : <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 master br0 state forwarding priority 32 cost 4
    hairpin off guard off root_block off fastleave off learning on flood on mcast_flood on 
 ''95: vnet0'' state UNKNOWN : <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 master br0 state forwarding priority 32 cost 100
    hairpin off guard off root_block off fastleave off learning on flood on mcast_flood on
 '''harley$'''


Let's have a look at flooding on the interfaces. I disable it on the physical interface enp1s0 of the bridge and reboot the guest:
 '''harley$''' sudo bridge link set dev enp1s0 flood off
 '''harley$'''
The guest gets an IP-Address from the DHCP-Server but then can't ping its gateway. DHCP-REQUEST is broadcast and goes thru enp1s0. DHCP-ANSWER comes back thru it to any other (here only vnet0) interface which has flood on. Ping is unicast and isn't forwareded on enp1s0. If I set  enp1s0 flood on and vnet0 flood off and <code>'''deb9-test$ '''sudo systemctl restart systemd-networkd</code>, I get no IP-Address from DHCP-Server and can't ping the interface. Incoming DHCP-ANSWER isn't broadcast and vnet0 doesn't forward it to the guest.

Btw. this method has bad performance as we can see with monitor. We insert MAC-Addresses into FDB for just deleting it immediately, all for nothing.
 '''harley$''' sudo bridge monitor fdb
 52:54:00:01:76:20 dev enp1s0 master br0 
 52:54:00:b0:ca:63 dev vnet0 master br0 
 f4:f2:6d:2c:87:f7 dev enp1s0 master br0 
 00:80:3f:2a:31:1a dev enp1s0 master br0 
 Deleted 52:54:00:01:76:20 dev enp1s0 master br0 stale
 Deleted 52:54:00:b0:ca:63 dev vnet0 master br0 stale
 Deleted 00:80:3f:2a:31:1a dev enp1s0 master br0 stale
 Deleted f4:f2:6d:2c:87:f7 dev enp1s0 master br0 stale
 ...

=== References ===
* https://www.freedesktop.org/software/systemd/man/systemd.netdev.html
* https://www.freedesktop.org/software/systemd/man/systemd.network.html

== linux bridge with libvirt hook scripts ==
We setup a bridge with VLAN enabled:
 '''harley$''' cat 08-br0.netdev 
 [NetDev]
 Name=br0
 Kind=bridge
 [Bridge]
 DefaultPVID=none
 VLANFiltering=true
 STP=false
 '''harley$''' cat 12-br0_add-enp1s0.network 
 [Match]
 Name=enp1s0
 [Network]
 Bridge=br0
 [BridgeVLAN]
 VLAN=10
 [BridgeVLAN]
 VLAN=20
 [BridgeVLAN]
 VLAN=30
 '''harley$''' cat 16-br0_up.network 
 [Match]
 Name=br0
With this I get:
 '''harley$''' sudo bridge vlan show
 port    vlan ids
 enp1s0   1 PVID Egress Untagged
          10
          20
          30  
 br0      1 PVID Egress Untagged
 '''harley$'''
But what is this? We have default VLAN <code>1 PVID Egress Untagged</code>. I don't want this. Seems setting <code>DefaultPVID=none</code> in 08-br0.netdev doesn't work. I've made a [[#Workaround for setting DefaultPVID=none|Workaround for setting DefaultPVID=none]]. Looking at this behavior I found that we can set <code>default_pvid</code> in the kernel only if <code>vlan_filtering = 0</code>. By hand I have to do:
 '''harley$''' sudo bash -c 'echo 0 >/sys/class/net/br0/bridge/vlan_filtering'
 '''harley$''' sudo bash -c 'echo 0 >/sys/class/net/br0/bridge/default_pvid'
 '''harley$''' sudo bash -c 'echo 1 >/sys/class/net/br0/bridge/vlan_filtering'
 '''harley$'''
If I start a guest I will get now:
 '''harley$''' virsh start deb9-test
 '''harley$''' sudo bridge vlan show
 port    vlan ids
 enp1s0   10
          20
          30
 br0     None
 vnet0   None
 '''harley$'''
The virtual network interface vnet0 for deb9-test has no VLAN ID. Libvirt does not know something about this so we have to tell it. Libvirt provides [https://www.libvirt.org/hooks.html hook scripts] that we can use for this. We have to:
# [[#define VLAN-ID the virtual machine belongs to]]
# [[#get information on startup from the runtime XML-config of the domain]]
# [[#set VLAN-ID to the dynamic virtual network interface vnet*]]
<span id="debug.sh">For debugging the hook-scripts</span> I've made a small script:
 '''harley$''' cat debug.sh
 #!/bin/bash -e
 # https://www.libvirt.org/hooks.html
 # If you make a new hook script then 'sudo systemctl restart libvirtd'.
 # For debug set symlink to hook-script daemon, qemu, lxc, libxl and/or network,
 # e.g. 'sudo ln -s debug.sh qemu' and restart libvirtd.
 
 logfile='/var/log/libvirt/hooks.log'
 
 echo "$0" >>$logfile
 date -Iseconds >>$logfile
 echo "\$1=$1, \$2=$2, \$3=$3, \$4=$4" >>$logfile
 cat - >>$logfile
 echo -e "\n---------------------------------------------" >>$logfile
 '''harley$'''

=== define VLAN-ID the virtual machine belongs to ===
For this we have an extra [https://libvirt.org/formatdomain.html#elementsMetadata element <metadata> in Domain XML format] for custom metadata. We can simply add the information to the static configuration with <code>'''harley$''' virsh edit deb9-test</code> like this (look only at the <metadata> element):
 '''harley$''' virsh dumpxml deb9-test | head -n9
 <domain type='kvm' id='1'>
   <name>deb9-test</name>
   <uuid>70d56a28-795d-4010-9403-513a4bd6b66a</uuid>
   <metadata>
     <my:home xmlns:my="http://hoeft-online.de/my/">
       <my:vlan>10</my:vlan>
     </my:home>
   </metadata>
   <memory unit='KiB'>1048576</memory>

=== get information on startup from the runtime XML-config of the domain ===
It seems a little bit difficult to get needed information out of the big XML-config but it's no problem with XSLT. I've made a XSL-stylesheet for this and use xmlstarlet. Start a virtual machine and then its runtime configuration is available with <code>'''harley$''' virsh dumpxml deb9-test | xmlstarlet tr qemu.xsl</code>. With this I can test my stylesheet. Here is it:
 '''harley$''' cat qemu.xsl 
 <?xml version="1.0" encoding="UTF-8"?>
 &lt;!-- This stylesheet extracts the VLAN-ID and the target device of the
      bridge from the domain-xml given to the libvirt hook-script "qemu".
      Example output: <meta><vlan>10</vlan><dev>vnet0</dev></meta>
 --&gt;
 <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
      xmlns:my="http://hoeft-online.de/my/" exclude-result-prefixes="my">
   <xsl:output omit-xml-declaration="yes" indent="no"
        encoding="utf-8" media-type="text/xml"/>
   <xsl:strip-space elements="*"/>
   <xsl:template match="text()|@*"/>
 
   <xsl:template match="/domain">
     <meta>
       <xsl:apply-templates/>
     </meta>
   </xsl:template>
 
   <xsl:template match="metadata/my:home/my:vlan">
     <vlan>
       <xsl:value-of select="."/>
     </vlan>
   </xsl:template>
 
   <xsl:template match='interface[@type="bridge"]/target'>
     <dev>
       <xsl:value-of select="@dev"/>
     </dev>
   </xsl:template>
 
 </xsl:stylesheet>
 '''harley$'''

 '''harley$''' virsh dumpxml deb9-test | xmlstarlet tr /etc/libvirt/hooks/qemu.xsl 
 <meta><vlan>10</vlan><dev>vnet0</dev></meta>'''harley$'''

=== set VLAN-ID to the dynamic virtual network interface vnet* ===
Putting it all together here is the executable hook-script:
 '''harley$''' cat /etc/libvirt/hooks/qemu
 #!/bin/bash
 #/etc/libvirt/hooks/qemu
 # Docs: https://www.libvirt.org/hooks.html
 # If you make a new hook script then 'sudo systemctl restart libvirtd'.
 
 # On startup of the domain (guest) This script does:
 # Get Metadata VLAN-ID of the guest and target device of the bridge from
     # the domain-xml available on standard input. It is the runtime
     # version from 'virsh dumpxml domainname'. For extracting the
     # information we use a XSL-stylesheet. Example input into $META:
     # <meta><vlan>10</vlan><dev>vnet0</dev></meta>
 # Select $DEV  from $META
 # Select $VLAN from $META
 # Set $VLAN to $DEV on the bridge
 
 case "$2" in
   prepare)
     ;;
   start)
     META=$(/usr/bin/xmlstarlet tr /etc/libvirt/hooks/qemu.xsl -)
     DEV=$(echo "$META" | /usr/bin/xmlstarlet sel -t -v '/meta/dev')
     VLAN=$(echo "$META" | /usr/bin/xmlstarlet sel -t -v '/meta/vlan')
     if &#91;[ -n $DEV && -n $VLAN ]&#93;; then
       /sbin/bridge vlan add vid "$VLAN" dev "$DEV"
     fi
     ;;
   started)
     ;;
   stopped)
     ;;
   release)
     ;;
   migrate)
     ;;
   restore)
     ;;
   reconnect)
     ;;
   attach)
     ;;
   *)
     echo "qemu hook called with unexpected options $*" >&2
     exit 1
     ;;
 esac
 '''harley$''' sudo chmod 744 /etc/libvirt/hooks/qemu
 '''harley$'''

=== References ===
* https://www.libvirt.org/hooks.html
* https://serverfault.com/questions/696011/libvirt-hook-qemu-suse12

== Workaround for setting DefaultPVID=none ==
<span style="color:red">We do not need it anymore. This bug is fixed in systemd 234.</span>

Setting [https://www.freedesktop.org/software/systemd/man/systemd.netdev.html#DefaultPVID= DefaultPVID] in a<code>systemd-networkd</code> configuration file to "none" does not work. Until this bug is fixed I've made a workaround. The kernel accepts setting <code>default_pvid</code> to 0 (means "none") only if <code>vlan_filtering=0</code>, so we have to do:
 '''harley$''' sudo bash -c 'echo 0 >/sys/class/net/br0/bridge/vlan_filtering'
 '''harley$''' sudo bash -c 'echo 0 >/sys/class/net/br0/bridge/default_pvid'
 '''harley$''' sudo bash -c 'echo 1 >/sys/class/net/br0/bridge/vlan_filtering'
 '''harley$'''
Check with listing of [[#bridge-settings|bridge-settings]].
Theese commands must run with <code>systemd-networkd</code> so we need a service for this. First I make a script and make it executable for root:
 '''harley$''' cat /etc/systemd/network/DefaultPVID.sh 
 #!/bin/bash
 #echo "entering DefaultPVID.sh" >>/tmp/debug.log
 
 BRDIR="/sys/class/net/br0/bridge/"
 
 if &#91;[ -f $BRDIR/vlan_filtering && -f $BRDIR/default_pvid ]&#93;; then
   #echo "setting DefaultPVID" >>/tmp/debug.log
   VLAN_FILTERING="$(cat "$BRDIR"/vlan_filtering)"
   echo 0 >"$BRDIR"/vlan_filtering
   echo 0 >"$BRDIR"/default_pvid
   echo "$VLAN_FILTERING" >"$BRDIR"/vlan_filtering
 fi
 exit 0
 '''harley$''' sudo chmod 744 /etc/systemd/network/DefaultPVID.sh
 '''harley$'''
Test with <code>'''harley$''' sudo /etc/systemd/network/DefaultPVID.sh</code>. Next I create a service to execute this script:
 '''harley$''' cat /etc/systemd/system/DefaultPVID.service 
 [Unit]
 Description=set DefaultPVID on a bridge as workaround
 Wants=network.target
 After=network.target
 
 [Service]
 Type=oneshot
 ExecStart=/etc/systemd/network/DefaultPVID.sh
 
 [Install]
 WantedBy=multi-user.target
 '''harley$'''
Test with <code>'''harley$''' sudo systemctl start DefaultPVID.service && systemctl status DefaultPVID.service</code>. After this I create a [https://www.freedesktop.org/software/systemd/man/systemd.unit.html#id-1.11.3 drop-in file for overriding vendor settings] so this service will be executed together with <code>systemd-networkd</code>:
 '''harley$''' cat /etc/systemd/system/systemd-networkd.service.d/DefaultPVID.conf 
 [Unit]
 # This is only a workaround. DefaultPVID cannot be set in
 # /etc/systemd/network/br0.netdev. It seems buggy.
 Wants=DefaultPVID.service
 Before=DefaultPVID.service
 '''harley$'''
Test with <code>'''harley$''' sudo systemctl restart systemd-networkd</code>.

[[Category:Virtualization]]