Ask Your Question

Revision history [back]

click to hide/show revision 1
initial version

Is the MAC address of a VM the same as the corresponding tap interface?

I have a single node openstack install on an ubuntu machine. For some reason that I cannot figure out, the linuxbridge is dropping packets from this VM. My iptables seem to be fine (atleast as far as I cam make out) and there are no ebtables chain rules configured.

I flushed my iptables and tried the same test and the packets are still being dropped.

While trying to debug the linuxbridge I found the following which confused me:

port no mac addr        is local?   ageing timer
  2 52:54:00:88:a3:cd   no        51.68
  2 52:54:00:95:96:8d   no        51.92
  2 52:54:00:b0:01:97   no        51.85
  2 52:54:00:dc:48:fe   no        43.01
  2 52:54:00:e5:fd:45   no         0.95
  2 52:54:00:e9:47:79   no        51.74
  2 52:54:00:f5:a4:d7   no        52.11
  2 54:26:96:33:20:5d   no         9.22
  2 60:c5:47:0a:2d:64   no         0.00
  2 64:70:02:c8:dc:fc   no         2.16
  2 6c:88:14:86:7e:38   no        47.86
  1 6e:0e:09:98:eb:c8   yes        0.00
  2 70:56:81:b1:d7:01   no        51.61
  2 7a:1c:08:d5:79:29   no        51.44
  2 84:38:35:5b:47:42   no       177.32
  2 88:1f:a1:13:72:4a   no        50.90
  2 90:27:e4:f1:e0:49   no         2.87
  2 94:de:80:20:3d:44   no         6.41
  2 94:de:80:20:3d:72   no        51.78
  2 94:de:80:bc:75:e7   no        52.06
  2 96:80:a0:ee:9c:c4   no        51.70
  2 96:d3:69:64:0d:36   no        51.35
  2 98:fe:94:46:b1:2c   no       229.38
  2 9c:4e:36:99:5d:e0   no         0.64
  2 aa:cd:61:6e:d3:fc   no        51.82
  2 ae:e6:a5:b0:c9:c9   no        51.58
  2 b2:1a:3a:25:b9:49   no        51.68
  2 b8:e8:56:45:7a:8a   no        51.76
  2 c6:db:db:8e:79:73   no        52.20
  2 ca:fe:ba:be:e3:01   no        10.11
  2 cc:3a:61:1e:e8:41   no        33.62
  2 de:ad:00:01:00:00   no        49.29
  2 de:ad:00:01:00:05   no        51.29
  2 de:ad:00:01:00:06   no        49.08
  2 e6:f6:a1:89:ff:96   no        51.46
  2 f4:f9:51:dd:3c:e1   no        22.08
  2 f6:6e:18:81:e7:c5   no        52.17
  2 f6:76:41:dc:97:88   no        52.09
  3 **fa:16:3e:1a:20:37**   no        51.29
  1 fa:16:3e:39:83:aa   no         2.16
  3 **fe:16:3e:1a:20:37**   yes        0.00

The last entry and the 2nd last mac are the same with one being local and the other not local.

This Mac corresponds to the eth0 mac address of one of my VMs:

I verified this by logging on to the console and doing "ip a"

This mac address also happens to be the MAC of the tap interface created on the host:

ifconfig tap3869edb5-6e
tap3869edb5-6e Link encap:Ethernet  HWaddr fe:16:3e:1a:20:37  
          inet6 addr: fe80::fc16:3eff:fe1a:2037/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:95102 errors:0 dropped:0 overruns:0 frame:0
          TX packets:3216620 errors:0 dropped:198 overruns:0 carrier:0
          collisions:0 txqueuelen:500 
          RX bytes:6852603 (6.8 MB)  TX bytes:352453624 (352.4 MB)

Is this the way it is supposed to be?

Any ideas on how to debug packets being dropped on the linuxbridge?

I am pinging the IP of the bridge interface from inside the VM. I have added the tap interface of the VM directly to the same bridge (using brctl add/delif).

I see the packets on the tap interface (using tcpdump), but they never make their way to the bridge interface.

Thanks!