Hi,
First of all - I am afraid no one has pointed it out so far - the entire hassle about PVST+ and IEEE interoperation comes into play if and only if we are looking at PVST+ operation at trunk ports. Normal access ports on Catalyst switches always emit and process standard IEEE STP BPDUs according to the access VLAN they are configured into.
Peter, great stuff! Can you tell me where I can find such information
regarding all the differences between Cisco implementation of STP and
non-Cisco switches?
The differences? Well, years of sitting in the lab, sniffing all packets going around No, really, Leo has provided a nice set of links in one of his recent posts in this thread, and I have included yet another link that is specific to the PVST+/IEEE STP interoperation - I am including it here again just for the sake of having things in place:
http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00801d11a0.shtml#topic1
So what youre saying on a igher level is that the
Cisco switches do NOT seamlessly interoperate with bridges that only run
IEEE STP, correct?
Well, perhaps I am too strict on the word selection after all. What I wanted to say is that regarding the PVST+/RPVST+ alone, IEEE switches ignore it because the BPDUs are encapsulated differently and addressed differently than IEEE STP BPDUs. The PVST+/RPVST+ BDPUs are tunelled through IEEE switches as if the entire IEEE-compliant switching domain was just a wire. However, each Catalyst switch, in parallel to PVST+/RPVST+, emits a standard IEEE STP BPDU to speak to IEEE-compliant neighboring switch, and that is where the interoperation takes place.
Also see the following document, it is also describing the PVST+ specifics:
http://www.cisco.com/en/US/docs/ios/lanswitch/configuration/guide/lsw_vlan_cfg_rtg_ps6441_TSD_Products_Configuration_Guide_Chapter.html#wp1006491
for a NON-MST solution, the Cisco switches can be left in PV mode, as
you dont have an "IEEE" choice anyway, BUT they will seamlessly operate
with the non-Cisco blade switches. But for this to happen, your Cisco
environment must have each distro switch configured as the bridge for
all VLANs. Correct with all this?
Yes. If the 802.1Q-encapsulated PVST+ BPDUs are to be tunneled through the IEEE region correctly, then all VLANs must be known to all switches. The IEEE STP BPDUs will be well understood by the IEEE neighbors, though.
As for MST, the same holds true, right? You cannot just configure an MST
region between the blade switches and the Cisco ToR and leave the rest
of the environment configured as it was before. The distro switches will
have to be reconfigured for MST, too. Correct?
Basically, yes - introducing yet another MSTP variant into a part of the network would only further complicate things. It would be ideal if all switches spoke MSTP, as Leo has correctly pointed out in his earlier post.
But - looking through the thread, I am not quite sure what problem we are trying to solve. You have said in your first post here that you have "STP issues". Can you be more specific about that?
Best regards,
Peter
