Cisco and Non-Cisco Spanning Tree Integration

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May 27th, 2010
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I have Dell Power Connect switches in a server farm's access layer and I need to run L2 uplinks to a Cisco top-of-rack switch.


The Power Connect only runs the IEEE flavors of STP and doesnt run per-vlan STP, as it is Cisco proprietary.


What would be the best way to integrate the Dells with regard to STP?


The Dells run STP rSTP and MST.


Correct me if I am wrong, but all of Cisco's implemetation's of STP are done on a per-vlan basis - pvst+.So, I dont think i can run IEEE Rapid STP with Cisco's implementation of RSTP, which is PVRST+. Correct?


I think the only exception would be MST, which would group vlans together in one region/instance.


Thanks

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lamav Thu, 05/27/2010 - 14:24
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Hi I dont understand that answer..


Thanks

lamav Thu, 05/27/2010 - 20:53
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Hellooooooooooooooooooooo


Anybody home? lol :-)

Ganesh Hariharan Thu, 05/27/2010 - 21:20
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I have Dell Power Connect switches in a server farm's access layer and I need to run L2 uplinks to a Cisco top-of-rack switch.


The Power Connect only runs the IEEE flavors of STP and doesnt run per-vlan STP, as it is Cisco proprietary.


What would be the best way to integrate the Dells with regard to STP?


The Dells run STP rSTP and MST.


Correct me if I am wrong, but all of Cisco's implemetation's of STP are done on a per-vlan basis - pvst+.So, I dont think i can run IEEE Rapid STP with Cisco's implementation of RSTP, which is PVRST+. Correct?


I think the only exception would be MST, which would group vlans together in one region/instance.


Thanks

Hi,


With interoperabilty of vendor environement and stp to use like in your case as Dell and cisco. As you said Dell PowerConnect switches have STP

enabled by default. However, for most efficient integration of PowerConnect switches into existing Cisco networks, RSTP mode will allow much faster network convergence.Follow the below steps to do the same :-

1)  Force the speed and duplex settings on all switch uplink ports

2)  Enable STP with RSTP mode on all Dell PowerConnect switches

3)  Enable STP on all Cisco devices (this is the default)


Note: Cisco Switches (and most other midrange Cisco switches) have Cisco’s proprietary Per-VLAN Spanning Tree Protocol (PVST+) enabled by default. However, Cisco switches will revert to using 802.1D STP with a peer switch after receiving a BPDU.


I suppose rather MST configuration you can go with STP with RSTP in dell switches.


Hope to Help !!


Ganesh.H

lamav Thu, 05/27/2010 - 21:49
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Ganesh, this is an interesting answer! Thanks..


Now let me see if I got this right...


You can run RSTP (IEEE 802.1W) on the Dell switches and IEEE 802.1D (STP) on the Ciscos because the Ciscos are backward compatible? Wont there be a mismatch with RSTP on one switch and STP on the other? Can you do that?


Is it possible to run IEEE 802.1W on Cisco switches - in other words, RSTP, not PVRSTP

Ganesh Hariharan Thu, 05/27/2010 - 22:00
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Ganesh, this is an interesting answer! Thanks..


Now let me see if I got this right...


You can run RSTP (IEEE 802.1W) on the Dell switches and IEEE 802.1D (STP) on the Ciscos because the Ciscos are backward compatible? Wont there be a mismatch with RSTP on one switch and STP on the other? Can you do that?


Is it possible to run IEEE 802.1W on Cisco switches - in other words, RSTP, not PVRSTP


Hi,


Let me try to explain in more detail about the compatibilty of RSTP and STP, RSTP is designed to be compatible and interoperable with the STP.However, the advantages of the fast re-convergence, introduced by the RSTP are lost when it interoperate with STP bridges.


In order to ensure compatibility with STP bridges, each RSTP bridge listens on its ports for configuration messages having the STP format. When a port receives such configuration message it starts behaving as a standard 802.1d STP bridge port. Other ports continue to behave according the RSTP.

RSTP bridge port that is attached to the same LAN as a STP bridge transmits configuration messages in STP format and when it is needed, it generates TCN messages as well. This is necessary because the RSTP configuration messages are discarded by the STP bridges.


In addition, the port state transition timer is increased and messages with TC bit set are being propagated for a longer period to interoperate with the different filtering database flushing mechanism used by STP.


Hope to Help !!


Ganesh.H

lamav Sat, 05/29/2010 - 09:18
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Ganesh, sorry it took me so long to get back.


I appreciate your very helpful input.


Thank you

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