Network Design - Root and Non root bridges

[craigphillips1979]

Hi,

We have a network set-up as the below image. Where the switches have STP enable to handle the muliple paths for the data to flow.

What I would like to know is should the 2 bridges plugged into the same switch e.g Switch A (Bridge A and Bridge B) both be root bridges and (Bridge C and Bridge D) both be non root.

Or should for example, Bridge A be a root and Bridge C a non root and Bridge B a non root and Bridge D the root?

Similarly with the rest of the other bridges E, F, G and H

Thanks

[Joseph W. Doherty]

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Posting

Sorry, I've a bit confused by your diagram and question, as switches are really multiport bridges, so, to me, it's unclear the difference between switch A and bridge A.

In general, root bridges are selected so there's the minimum number of hops between any two network segments.  However,  if you "know" there especially heavy/reoccurring traffic between two network segment, you might setup your L2 topology to decrease the hops between those segments at the expensive of increasing the hops between other segments.

[craigphillips1979]

Hi,

At the moment Switch A is in the main office with all machines plugged into it, Bridges A + C and Bridges B + D are point-to-point links to a warehouse where Switch B resides, and this provides connectivity back to the main office. There are 2 links incase one of the links goes down.

At the moment Bridge A is the Root and Bridge C the non root for link 1.

Bridge B is the non root and Bridge D is the root for link 2.

What I was wondering was is this the correct set-up or should Bridge A and Bridge B both be the root  and Bridge C And D the non root devices? or does it not matter?

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

I'm sorry, I'm still confused.  Are your "bridge" devices actual just p2p links from the adjacent switches, or are they, themselves, actual bridges that are running L2 and are part of STP topology?  (What's confusing me, if they are real bridge devices, why do you need them?  I.e. why not p2p links between the switches, which are multiport bridges themselves?)

[craigphillips1979]

The bridges are Cisco Aironet 1300 Series Wireless Bridges (AIR-BR1310G-E-K9-R) with Yagi antennae. They are providing point-to-point links between the 2 locations. The Switch is running STP and decides which port is blocking and forwarding.

At the moment the switch (A) is forwarding out of the port to Bridge A  and blocking on the port that bridge B is plugged into.

[Joseph W. Doherty]

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

Ah, I think I understand.  So the wireless bridges are "transparent" to the rest of the network.  They just convert wired to wireless and back again.

If I have that right, we can ignore them and just consider your switches.

In that case, it appears you have two L2 loops, those formed by the dual paths between switches A and B and between switches C and D.  From a topology standpoint, it doesn't seem to matter what switch you select as root and secondary root.  However, as switches B and C are the interior switches, I would suggest those as your root and secondary root switches.

[craigphillips1979]

I think I understand what you are saying

Thanks

[Stuart Gall]

No matter how many bridges you configure as root only one will actually be the root for each vlan (pvst/rpvst)
If your bridges are wifi and hence quite slow you want to configure one of the switches to be the root bridge.

Sent from Cisco Technical Support iPad App

[Rasika Nayanajith]

Keep Bridge A & B configured as "root" & C& D as "not-root". In similar manner bridge E & F configure as root & G & H as non-root bridge. These are not refer to STP root & non-root in this toplogy. In otherwords these refer to AP role when establishing bridge connection.

Anyway due to STP one path get blocked always. From STP perspective it is good idea to switch A become STP root in your topology being it is in your main office.

HTH

Rasika

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