From: Marc Haber <mh+libvirt-users(a)zugschlus.de&gt; Subject: macvtap and tagged VLANs to the VM To: libvirt-users(a)redhat.com Date: Sun, 16 Dec 2018 22:59:22 +0100 User-Agent: Mutt/1.9.5 (2018-04-13) Hi, I would like to run a network firewall as a VM on a KVM host. There are ~ 25 VLANs delivered to the KVM host on three dedicated links, no LACP or other things. I have the VLANs 100-180 on the host's enp1s0, the VLANs 200-280 on the host's enp2s0 and the VLANs 300-380 on the host's enp3s0. To save myself from configuring all VLANs on the KVM host, I'd like to hand the entire ethernet link to the VM and to have the VLAN interfaces there. Using classical Linux bridges (brctl), things work fine. They don't when I try macvlan: On the host: 4: enp3s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000 link/ether 00:0d:b9:34:2a:fe brd ff:ff:ff:ff:ff:ff promiscuity 1 addrgenmode eui64 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535 5: unt382@enp3s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000 link/ether 00:0d:b9:34:2a:fe brd ff:ff:ff:ff:ff:ff promiscuity 0 vlan protocol 802.1Q id 382 <REORDER_HDR> addrgenmode eui64 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535 15: macvtap3@enp3s0: <BROADCAST,MULTICAST,ALLMULTI,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 500 link/ether 52:54:00:bf:bb:ab brd ff:ff:ff:ff:ff:ff promiscuity 0 macvtap mode bridge addrgenmode eui64 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535 4: enp3s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000 link/ether 00:0d:b9:34:2a:fe brd ff:ff:ff:ff:ff:ff inet6 fe80::20d:b9ff:fe34:2afe/64 scope link valid_lft forever preferred_lft forever 5: unt382@enp3s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000 link/ether 00:0d:b9:34:2a:fe brd ff:ff:ff:ff:ff:ff inet6 fe80::20d:b9ff:fe34:2afe/64 scope link valid_lft forever preferred_lft forever 15: macvtap3@enp3s0: <BROADCAST,MULTICAST,ALLMULTI,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 500 link/ether 52:54:00:bf:bb:ab brd ff:ff:ff:ff:ff:ff inet6 fe80::5054:ff:febf:bbab/64 scope link valid_lft forever preferred_lft forever In the XML: <interface type='direct'> <mac address='52:54:00:bf:bb:ab'/> <source dev='enp3s0' mode='bridge'/> <target dev='macvtap3'/> <model type='virtio'/> <alias name='net0'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/> </interface> And in the VM: root@grml ~ # ip -d link show 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 promiscuity 0 addrgenmode eui64 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000 link/ether 52:54:00:bf:bb:ab brd ff:ff:ff:ff:ff:ff promiscuity 0 addrgenmode eui64 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535 3: vlan0@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000 link/ether 52:54:00:bf:bb:ab brd ff:ff:ff:ff:ff:ff promiscuity 0 vlan protocol 802.1Q id 382 <REORDER_HDR> addrgenmode eui64 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535 root@grml ~ # ip a 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever inet6 ::1/128 scope host valid_lft forever preferred_lft forever 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000 link/ether 52:54:00:bf:bb:ab brd ff:ff:ff:ff:ff:ff inet6 fe80::5054:ff:febf:bbab/64 scope link valid_lft forever preferred_lft forever 3: vlan0@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000 link/ether 52:54:00:bf:bb:ab brd ff:ff:ff:ff:ff:ff inet 192.168.252.220/24 brd 192.168.252.255 scope global vlan0 valid_lft forever preferred_lft forever inet6 fe80::5054:ff:febf:bbab/64 scope link valid_lft forever preferred_lft forever root@grml ~ # I then ping from the VM to 192.168.252.241, which is a differnt host on the network, neither the VM host the VM is running on nor another VM on the same host. That should rule out the connectivity issues that a macvtap interface has, right? On the VM, I see ARP requests going out, but no answers come in. On the pinged host, I see: 22:50:23.881163 52:54:00:bf:bb:ab > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 192.168.252.241 tell 192.168.252.220, length 46 22:50:23.881242 52:54:00:95:df:a6 > 52:54:00:bf:bb:ab, ethertype ARP (0x0806), length 42: Reply 192.168.252.241 is-at 52:54:00:95:df:a6, length 28 So, the packets going out from my VM are correctly delivered to the target, the target replies, but the replies never make it back to the VM. Do I see correctly that tcpdump on the VM host won't give accurate readings since macvtap will divert the frame before tcpdump will see it? On the other hand, a VM directly configured to the host's unt382 interface works fine: <interface type='direct'> <mac address='52:54:00:cb:ed:34'/> <source dev='unt382' mode='bridge'/> <model type='virtio'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/> </interface> I would however like to avoid having 25 interface stanzas in my XML. I would appeciate any ideas to solve this issue. I know this is most probably not a libvirt issue, but this list is about the only place that comes to my mind where people knowledgeable about those complex network stuff might hang around. If there is a better place to ask, I am open for suggestion. Please pardon my intrusion. Greetings Marc -- ----------------------------------------------------------------------------- Marc Haber | "I don't trust Computers. They | Mailadresse im Header Leimen, Germany | lose things." Winona Ryder | Fon: *49 6224 1600402 Nordisch by Nature | How to make an American Quilt | Fax: *49 6224 1600421

On 12/16/18 4:59 PM, Marc Haber wrote: > I would like to run a network firewall as a VM on a KVM host. There are > ~ 25 VLANs delivered to the KVM host on three dedicated links, no LACP > or other things. I have the VLANs 100-180 on the host's enp1s0, the VLANs > 200-280 on the host's enp2s0 and the VLANs 300-380 on the host's enp3s0. > > To save myself from configuring all VLANs on the KVM host, I'd like to > hand the entire ethernet link to the VM and to have the VLAN interfaces > there. Using classical Linux bridges (brctl), things work fine. When I asked the person I go to with questions about macvtap (because he knows the internals), his response was "if a Linux host bridge works, then he should use that". In other words, he was skeptical that what you want to do could be made to work with macvtap.

Is there a specific reason you need to use macvtap than a Linux host bridge?

On 1/3/19 9:23 AM, Marc Haber wrote: > On Wed, Jan 02, 2019 at 11:34:30AM -0500, Laine Stump wrote: > > On 12/16/18 4:59 PM, Marc Haber wrote: > > > I would like to run a network firewall as a VM on a KVM host. There are > > > ~ 25 VLANs delivered to the KVM host on three dedicated links, no LACP > > > or other things. I have the VLANs 100-180 on the host's enp1s0, the VLANs > > > 200-280 on the host's enp2s0 and the VLANs 300-380 on the host's enp3s0. > > > > > > To save myself from configuring all VLANs on the KVM host, I'd like to > > > hand the entire ethernet link to the VM and to have the VLAN interfaces > > > there. Using classical Linux bridges (brctl), things work fine. > > > > When I asked the person I go to with questions about macvtap (because he > > knows the internals), his response was "if a Linux host bridge works, then > > he should use that". In other words, he was skeptical that what you want to > > do could be made to work with macvtap. > > I see. > > A Linux host bridge is what I build with brctl? Yes, although I wouldn't use the brctl command directly if I were you - much simpler an more stable to set it up in your host's system network config, and let initscripts/NetworkManager/whatever your distro uses take care of creating the bridge / attaching your physical ethernet each time the host boots.

> > Is there a specific reason you need to use macvtap than a Linux host bridge? > > I somehow got the impression that using macvtap is the more "modern" > and also more performant approach to bring network to VMs. Since the VM > in question is a Firewall, I'd love to have the performance impact > caused by virtualization minimized[1]. > > If this is a misconception, it might have been partially caused by some > colleagues at my last customer's site who very vocal about deprecating > the classical brctl bridges in favor of macvtap/macvlan, Not really. macvtap is useful because it's simple to setup (doesn't require a change to the host's network config), but is also problematic in some

ways, e.g. it doesn't allow host<->guest communication (unless you have a switch that reflects all traffic back to the sender).

These days use of macvtap for guest connection is more the exception than the rule.

> and the fact > that virt-manager uses macvtap by default and needs to be massaged into > allowing a classic brctl bridge. On my host that has a bridge named "br0", *that* is what is offered for connection of a new guest interface by default, not any macvtap interface.

And on another host that has no br0 device, libvirt's own "default" network is the default selection for new network devices, followed in the list by other libvirt virtual networks. In all cases, the selections for macvtap connections to the host's physical ethernets are included all the way at the bottom of the list, below both libvirt virtual networks *and* host bridges.