[ovs-discuss] VLAN, STP and physical switch

Ethan Jackson ethan at nicira.com
Thu Jul 5 20:05:37 UTC 2012


The cisco is using PVST (Per VLAN Spanning Tree), while OVS only
supports basic 802.1d.  You will either have to configure the cisco to
use 802.1d, or figure out if PVST has a compatibility mode.  Or, of
course, you could simply not build a loop thus making spanning tree
unnecessary.  In your diagram, if the cisco is chosen as the root, the
gre tunnel won't be used anyway.

Ethan

On Thu, Jul 5, 2012 at 9:20 AM, Maxime Brun <maxime at agretis.net> wrote:
> Hi,
>
> I am trying to interconnect several VMs and physical server, using ovs
> and physicals switches.
>
> An example :
>
> 2 ovs bridge (on separate physical server, interconnected with gre) with
> each 2 virtual interface (vm) and a vlan interface (eth1.140) ; both
> eth1 are directly connected to a physical switch (cisco 3750). I will
> try a schema :
>
>  vm1-2       vm3-4
>  _____  gre  _____
> |_ovs_|-----|_ovs_|
>     _|_______|_
>    |___3750____|
>          |
>          |
>  physical server
>
>
> The problem is with spanning tree. STP with ovs works well (there is one
> root bridge), but 3750 is also root. It seems there is 2 separate
> spanning tree domain.
>
> Using tcpdump, it seems they don't use the same protocol :
>
> 16:08:28.094021 00:19:56:72:ce:ad > 01:00:0c:cc:cc:cd, ethertype 802.1Q
> (0x8100), length 68: vlan 140, p 0, LLC, dsap SNAP (0xaa) Individual,
> ssap SNAP (0xaa) Command, ctrl 0x03: oui Cisco (0x00000c), pid PVST
> (0x010b): STP 802.1d, Config, Flags [none], bridge-id
> 708c.00:19:56:72:ce:80.802d, length 42
>
> 16:08:28.293259 00:21:5a:d4:15:31 > 01:80:c2:00:00:00, ethertype 802.1Q
> (0x8100), length 56: vlan 140, p 0, LLC, dsap STP (0x42) Individual,
> ssap STP (0x42) Command, ctrl 0x03: STP 802.1d, Config, Flags [none],
> bridge-id 8000.00:21:5a:d4:15:31.8004, length 35
>
> I didn't find any way to use the same spanning tree protocol.
>
>
> Am i wrong about this conf ? Any idea is welcome ...
>
>
> Thank you.
>
>
>
> Regards,
>
> Maxime
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