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

asked 2014-02-14 18:37:08 -0500

NetCubist gravatar image

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

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answered 2014-02-15 04:16:49 -0500

Mathias Ewald gravatar image

Nope tap MAC is not the same as eth0 MAC. I am not using linux bridge but I would suggest you check if you bridge interface is up. I had problems with interfaces being down a lot and still have after reboots. I ended upping every interface I could find a suddently worked. Now after every reboot of my network node I have to do "ip link set dev eth1 up" or it won't work :D

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Strangely I have several VMs that work just fine. They all have their eth0 MAC same as the tap MAC. The strange thing is that even on the VM that has this issue, it successfully gets an IP address from a DHCP server via the bridge (in other words bcast works), but at the same time arp does not work.

NetCubist gravatar imageNetCubist ( 2014-02-15 19:22:10 -0500 )edit

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Asked: 2014-02-14 18:37:08 -0500

Seen: 902 times

Last updated: Feb 15 '14