[ovs-discuss] Confused how to set up an STP loop topology on BPI switches

Raymond Burkholder ray at oneunified.net
Wed Jan 9 18:00:06 UTC 2019

On 2019-01-09 8:33 a.m., Christopher Hannon wrote:
> Thanks for your reply, I think I understand your point regarding 
> hardware switching. Although wouldn't there need to be a layer 3 
> connection somewhere to pull a packet from one vlan to the other? I 
> guess I am not completely sure about how the vlans get connected 
> together. Would this be in OVS?

Yes, then things become more of a layer 3 mechanism.  That is about all 
I've come up with when up against a lower level hardware switch.

Possibly in swconfig or the iproute2 or ethtool there is a mechanism to 
define them as access ports, each in their own vlan.  But VLAN ids are 
passed up in the skb structures, so  don't know if that would work.  
Maybe XDP performs operations before OVS picks up packets.  But that is 
getting deep into the weeds.

If you desire to use the default switch in OVS, then.... maybe very 
difficult.  I don't know if performing vlan pre-processing will help.  
Something along the lines of pushing/popping vlan tags as in


But if you use the openflow side of things and program in your own 
packet ops, you may get something closer.  But you won't have the STP 
side of things, unless you program that yourself as well.

> On Tue, Jan 8, 2019 at 10:00 PM Raymond Burkholder <ray at oneunified.net 
> <mailto:ray at oneunified.net>> wrote:
>     One solution might be to supply a unique vlan between each pair of
>     switches:
>     vlan 111 s1,sw2
>     vlan 112 sw2,sw3
>     vlan 114 sw3,sw4
>     vlan 115 sw4,sw1
>     I *think* the issue is that with the lan ports all in the same
>     vlan, the hardware switch is switching packets, and not passing
>     the packets up to ovs.  And if the hardware switch does not have
>     STP turned on, you will end up with the loop.
>     With the segregating vlans, packets should then be passed to OVS
>     for use in it's bridging functions.

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