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Spantree Options


could any one tell me what does the following means?

1-spanning-tree mode pvst.

2-spanning-tree loopguard default.

3-no spanning-tree optimize bpdu transmission.

4-spanning-tree extend system-id.

the above is written when I issue (sh run) on the Switch, and what is benefit of using (PVST+), how this option could be enabled on the Switch?


Re: Spantree Options

Hi Friend,

Let me try to explain

1) To switch between PVST+ and MST modes, use the spanning-tree mode command. To return to the default settings, use the no form of this command.

If you have this command "spanning-tree mode pvst" this means you are running pvst+

Here PVST specifies PVST+

2) To enable loop guard as the default on all ports of a specific bridge, use the spanning-tree loopguard default command.

Loop guard provides an additional security in the bridge network. Loop guard prevents alternate or root ports from becoming the designated port because of a failure leading to a unidirectional link.

Loop guard operates only on ports that are considered point-to-point by the spanning tree.

Individual loop-guard port configuration overrides this global default

3) "spanning-tree optimize bpdu transmission" enables the switch to send multiple BPDUs from the interrupt context thereby reducing the CPU usage for the transmission function.

so "no spanning-tree optimize bpdu transmission" will definmetely stop that.

Note that not all platforms support it.

4) To enable the extended system ID feature on a chassis that supports 1024 MAC addresses, use the spanning-tree extend system-id command.

Releases 12.1(13)E and later support chassis with 64 or 1024 MAC addresses. For chassis with 64 MAC addresses, STP uses the extended system ID plus a MAC address to make the bridge ID unique for each VLAN.

You cannot disable the extended system ID on chassis that support 64 MAC addresses.

Enabling or disabling the extended system ID updates the bridge IDs of all active STP instances, which might change the spanning-tree topology.

Benefit of PVST+ is running spanning tree instance per vlan and better and optimise paths to reach the root bridge. Currently you are running PVST+ only.

HTH, if yes please rate the post.