[libvirt-users] KVM-Docker-Networking using TAP and MACVLAN

[Lars Lindstrom]

Hi everyone!

I have the following requirement: I need to connect a set of Docker
containers to a KVM. The containers shall be isolated in a way that they
cannot communicate to each other without going through the KVM, which
will act as router/firewall. For this, I thought about the following
simple setup (as opposed to a more complex one involving a bridge with
vlan_filtering and a seperate VLAN for each container):

+------------------------------------------------------------------+
| Host |
|  +-------------+ +----------------------+---+
|  | KVM         |                      | Docker           +-> | a |
|  |  +----------+     +----------+     +--------------+ +---+
|  |  | NIC lan0 | <-> | DEV tap0 | <-> | NET macvlan0 | <-+-> | b |
|  |  +----------+     +----------+     +--------------+ +---+
|  |             |                      |                  +-> | c |
|  +-------------+ +----------------------+---+
| |
+------------------------------------------------------------------+

NIC lan0:
    <interface type='direct'>
       <source dev='tap0' mode='vepa'/>
       <model type='virtio'/>
    </interface>
    *** Welcome to pfSense 2.4.4-RELEASE-p1 (amd64) on pfSense ***
    LAN (lan) -> vtnet0 -> v4: 10.0.20.1/24

DEV tap0:
    [root at server ~]# ip tuntap add tap0 mode tap
    [root at server ~]# ip l set tap0 up
    [root at server ~]# ip l show tap0
    49: tap0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc
fq_codel state DOWN mode DEFAULT group default qlen 1000
        link/ether ce:9e:95:89:33:5f brd ff:ff:ff:ff:ff:ff
    [root at server ~]# virsh start pfsense
    [root at server opt]# ip l show tap0
    49: tap0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc
fq_codel state DOWN mode DEFAULT group default qlen 1000
        link/ether ce:9e:95:89:33:5f brd ff:ff:ff:ff:ff:ff

NET macvlan0:
    [root at server ~]# docker network create --driver macvlan
--subnet=10.0.20.0/24 --gateway=10.0.20.1 --opt parent=tap0 macvlan0

CNT a:
    [root at server ~]# docker run --network macvlan0 --ip=10.0.20.2 -it
alpine /bin/sh
    / # ping -c 4 10.0.20.1
    PING 10.0.20.1 (10.0.20.1): 56 data bytes
    --- 10.0.20.1 ping statistics ---
    4 packets transmitted, 0 packets received, 100% packet loss
    / # ifconfig
    eth0      Link encap:Ethernet  HWaddr 02:42:0A:00:14:02
              inet addr:10.0.20.2  Bcast:10.0.20.255 Mask:255.255.255.0
              UP BROADCAST MULTICAST  MTU:1500  Metric:1
              RX packets:0 errors:0 dropped:0 overruns:0 frame:0
              TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
              collisions:0 txqueuelen:0
              RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
    lo        Link encap:Local Loopback
              inet addr:127.0.0.1  Mask:255.0.0.0
              UP LOOPBACK RUNNING  MTU:65536  Metric:1
              RX packets:4 errors:0 dropped:0 overruns:0 frame:0
              TX packets:4 errors:0 dropped:0 overruns:0 carrier:0
              collisions:0 txqueuelen:1000
              RX bytes:448 (448.0 B)  TX bytes:448 (448.0 B)
    / # ip r
    default via 10.0.20.1 dev eth0
    10.0.20.0/24 dev eth0 scope link  src 10.0.20.2

CNT b:
    [root at server ~]# docker run --network macvlan0 --ip=10.0.20.2 -it
alpine /bin/ping 10.0.20.1
    PING 10.0.20.1 (10.0.20.1): 56 data bytes

CNT c:
    [root at server ~]# docker run --network macvlan0 --ip=10.0.20.2 -it
alpine /bin/ping 10.0.20.1
    PING 10.0.20.1 (10.0.20.1): 56 data bytes


The KVM is not reachable from within a Docker container (during the test
firewalld was disabled) and vice versa. The first thing I noticed is
that tap0 remains NO-CARRIER and DOWN, even though the KVM has been
started. Shouldn't the link come up as soon as the KVM is started (and
thus is connected to the tap0 device)? The next thing that looked
strange to me - even though interface and routing configuration within
the container seemingly looks OK, there are 0 packets TX/RX on eth0
after pinging the KVM (but 4 on lo instead).

Any idea on how to proceed from here? Is this a valid setup and a valid
libvirt configuration for that setup?


Thanks and br, Lars