If_bridge and MST

Shteryana Shopova syrinx at FreeBSD.org
Tue Sep 4 01:33:14 PDT 2007


On 9/4/07, Andrew Thompson <thompsa at freebsd.org> wrote:
> On Mon, Sep 03, 2007 at 10:21:20PM +0100, Tom Judge wrote:
> > Andrew Thompson wrote:
> > >On Mon, Sep 03, 2007 at 02:11:59PM +0100, Tom Judge wrote:
> > >>Hi,
> > >>
> > >>I was wondering if if_bridge had been taught how to speak multiple
> > >>instance spanning tree?
> > >
> > >Not yet. I havnt started it yet and I do not know of anyone else working
> > >on it.
> > >
> > While playing with if_bridge today and a pair of Dell PowerConnect
> > 5324's (with the recent upgrade to MSTP) I noticed that it did not seem
> > to be possible to enable STP on if_vlan bridge members.  This would seem
> > to be correct as transmitting STP frames tagged with VLAN_ID would seem
> > to break the spec and fall into the realm of cisco PVST.  However should
> > if_bridge be taught that the vlandev should be used for collection and
> > transmission spanning tree in this scenario or should if_vlan be taught
> > to copy untagged [R]STP frames onto the vlan interface?
>
> Would this make it work the same as Cisco PVST? I havnt looked into how
> PVST works but whatever the solution is it would need to interoperate
> with other vendors. Obviously MST support is ideal. Most of the code is
> already there in the form of RSTP, and MST tacks a bit more info on the
> end. To be honest I have found 802.1Q-2003 a bit unclear in this area.
>
>

AFAIK, Cisco PVST is the predecessor of 802.1Q MSTP. If I remember
correctly one of the notable differences between the two is that with
Cisco PVST BPDUs are send for every spanning tree instance (also
tagged?) while with 802.1Q MSTP all information is contained in the
per instance M-records (MSTI Configuration Messages) in a single BPDU,
and BPDUs are only sent in instance 0.

cheers,
Shteryana


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