Rapid STP -- MST

Unanswered Question
Mar 15th, 2010

Hello,


I am runnig MST (Multiple instance spanning tree) in my network. When I connect switch with Rapid STP at the edge of MST region, status of spanning tree on that link depends on the connected device.


for instance:


MST REGION SWITCH <----> CATALYST 2960 with Rapid PVST then on MST switch can be seen P2P (boundary PVST+). As it should be.


MST REGION SWITCH <-----> LINKSYS SRW224P with Rapid STP then on MST switch can be seen P2P. Sometimes even P2P pre STD


It seems that Cisco recognize Linksys runnig IEEE Rapid STP as Internal (as if it runs MST).

Since Linksys runs IEEE Rapid STP, is there maybe some known issue when Cisco MST switch is connected to IEEE Rapid STP?


And just one question not related to the one above.

When MST region is connected to IEEE STP non-Cisco switch  (which is properly detected on MST switch as p2p boundary STP), and when STP switch sends TCN into MST region, shouldn't that TCN BPDU inside of MST be proccessed only in MST0?

Because I can see in lab that all three, MST0, MST1 and MST2, are in toppology change state at a same time if some port goes up on IEEE STP switch.


Thank you and regards,

A.

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Paolo Bevilacqua Mon, 03/15/2010 - 04:12

Recommend use only true Cisco switches in enterprise networks.

Other consumer brands, including Linksys, are not sophisticated enough and will not do anything to correct any problem you may find.

Giuseppe Larosa Mon, 03/15/2010 - 07:38

Hello Antonio,

if linksys executes IEEE 802.1W it should be correct to see it as the IST / MST 0.


Also the fact that all instances are involved when a TCN is sent by link from non cisco switch should be correct, the link can be a trunk allowing all vlans, so it is not known before what MST instances are affected


what Paolo says is agreable: linksys is not targeted for enteprise use.


Hope to help

Giuseppe

Antonio_1_2 Mon, 03/15/2010 - 10:27

Hi Giuseppe


I aggree about Linksys, but on the other hand if it executes (standard) IEEE Rapid STP, it should work according to standard. It doesn't metter if it is intended for SOHO or Enterprise market.


Regarding the second question, if MST switch is connected to IEEE STP (only one instance is executed on switch, it is not PVST), MST should comminicated with that switch via MST0.

Is that according to standard that when TCN is sent from IEEE STP switch toward MST switch that MST0, MST1 and MST2 is in topologychange state ( I thought only MST0 should be in topologychange state (and that shouldn't be so important because MST0 doesn't contain any VLAN)?

(that is if all VLANs are allowed)?.

Even so, since only one instance is runnig on IEEE switch, it shouldn't metter if all VLANs allowed or only one? Am I thinking correct?


Thank you,

A.

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