[c-nsp] Cisco MSTP - PVSTP question

[mihai at duras.ro]

Hello,


Thanks for the advice.
Seems I was sloppy and was missing a vlan from those 1-10.


I no longer have that uplink blocked.



> Hi Mihai,
>
> To achieve you goal.
>
> You must place 1-10 vlans on C2 and C3 to the MST0 instance.
> Such way C1 can be root for this vlans.
>
> For all others vlans C2 or C3  can be a root.
>
> You are right that " all  communication
> with the PVST is done via the IST-CST instance"
>
>
>
> -----------------------
> Sincerely Yours,
> Konstantin Fedorov
>
> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net
> [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Mihai Tanasescu
> Sent: Tuesday, September 19, 2006 3:18 AM
> To: cisco-nsp at puck.nether.net
> Subject: [c-nsp] Cisco MSTP - PVSTP question
>
> Hello,
>
>
>
> I saw some previous topics in the cisco-nsp archive regarding MSTP and
> PVSTP interaction but I still have some uncertainties.
> Also I've read the "understanding MSTP article" from cisco's website.
>
>
> I've setup a test scenario with the following configuration:
>
>
> C1 Cisco PVST  ---- C2 MST ---- C3 MST non-cisco switch (doesn't know
> PVSTP)
>
> C1 has vlans 1-10 for which it must necessarily be root bridge
>
> C2 must be root bridge for all other vlans
>
> C3 will transport 1-10 + the other vlans
>
> C1 can not be migrated to MST while C2 if possible should interoperate
> with the non-cisco MST enabled switch.
>
> What I have done:
>
> Setup 1:
>
> C2 mst root bridge for all vlans
> C3 learnt of C2 being the root bridge
> C1 the PVST also learnt this (as far as I've read all  communication
> with the PVST is done via the IST-CST instance)
>
> Although this worked just fine, unfortunately it wasn't what I was
> searching for.
>
>
> Setup 2:
>
> C1 -- C2
>
> C1 lower priority for vlans 1-10 (disabled spanning tree on the other
> vlans / or removed them from the trunk to C2 if not required to be
> present there)
>
> C2 reported:
>
> SPANTREE-2-ROOTGUARD_UNBLOCK: Root guard blocking port ...
>
> And the port was shown as blocked in both the IST0 and the other MSTIs.
>
> I've also tried the alternate configuration (not recommended) from:
> http://www.cisco.com/warp/public/473/147.html#alternate_configuration
> without any luck.
>
> Disabling PVSTP on the C1 interface to C2 of course made the C2 port to
> be removed from blocking as expected.
>
> I have several questions in regard to this:
>
> a) Why are both IST0 and the boundary ports for the MSTIs placed in
> Blocking ?
>
> b) According to that article shouldn't there be a way to have the PVST
> be root bridge for all the instances present on it ?
>
> c) What alternate setup could there be possible to achieve the
> redundancy desired while maintaining
> C1 root bridge for vlans 1-10
> C2 root bridge for the others
> C3 interoperability with C2 (C3 only knows MST and RSTP)
>
>
>
> Any advice would be appreciated.
>
>
> Thanks,
> Mihai
>
>
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