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Community Member

Rapid spanning tree combnation

Dear All,

I am new to Spanning tree technology...and it sounds pretty good to run 802.w on LAN,

Is it posible to run 802.w on switches that support Rapid spanning tree and some old ones that do not ?

Is there any way to prevent BPDU to be send to switch that do not support 802.w ?

Looking forward to hearing from you??

Best regards,

Sholeh

3 REPLIES
Community Member

Re: Rapid spanning tree combnation

802.w can interact fine with older spanning-tree versions. Only there will be no fast Covergence to the switch running the old spanning-tree.

See also:

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfa.shtml

Community Member

Re: Rapid spanning tree combnation

Dear All,

In our network I also employ Switch Catalyst C5500...which makes me confuse to identfy port's role as root port or as designated port...?

when I run show spantree it shows status..forwarding.

Can anyone brighten this darkness ?

Best regards,

Sholeh

Re: Rapid spanning tree combnation

The roles were in fact introduced by RSTP. Because it was also very convenient with regular STP, we added them to our implementation of STP. However, older software are just showing the information defined in STP at that time.

A forwarding port is indeed designated or root. In order to make a difference between the two, you need to check what is the designated bridge ID. If this is the local bridge, the port is designated. If it's a different bridge, it's a root port.

Another simple way: you also get the root port for the vlan in the show spantree. There is only a maximum of one root port on a bridge, so if your forwarding port is not the root port, it is then designated.

Note that STP does not make any difference between backup and alternate port either. For this, you need again to look for the designated bridge ID on this port. If it is the bridge itself, this is a backup port, else, an alternate port (this is useful for uplinkfast, only alternate port can do fast transition).

Regards,

Francois

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