Date: Tue, 04 Sep 2007 09:38:41 +0100 From: Tom Judge <tom@tomjudge.com> To: syrinx@FreeBSD.org Cc: Andrew Thompson <thompsa@freebsd.org>, net@freebsd.org Subject: Re: If_bridge and MST Message-ID: <46DD1991.1080104@tomjudge.com> In-Reply-To: <61b573980709040107t490632far990da52e5bfea3a1@mail.gmail.com> References: <46DC081F.6010203@tomjudge.com> <20070903173435.GA9902@heff.fud.org.nz> <46DC7AD0.4080800@tomjudge.com> <20070903210005.GA14592@heff.fud.org.nz> <61b573980709040107t490632far990da52e5bfea3a1@mail.gmail.com>
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Shteryana Shopova wrote: > On 9/4/07, Andrew Thompson <thompsa@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 Yes this seems correct from what I have read, there is an instance for every VLAN, and BPDU's are transmitted tagged on each VLAN. In MST instance 0 is the default instance and RSTP BPDU's are transmitted untagged on the interface, other instance data is attached to the instance 0 BPDU's as described. Tom
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