spanning-tree

I learned something about STP tonite I'd like to share.

You can enable BPDU guard in 2 ways.

1) configuration mode
spanning-tree portfast bpduguard

This will enable the protection on all interfaces already setup in portfast mode.

2) However you can't use the same command within the interface mode itself as it's different. This is what irks me!

Anyways, to enable it on the interface itself, the command is:

spanning-tree bpduguard enable

Also another tip. In STP, the hello BPDU's occur every 2 seconds coming from the root down. The switches then forward the BDPU's to other switches. But in RSTP, all switches provide the BPDU's every 2 seconds regardless of what the root switch does....

Back to STP, if the switches don't get the hellos from the root, they don't do anything as far as letting other switches know....

I'm pretty sure that's correct, feel free to point out any areas I'm off on...

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Comments

mgeorge

I'm curious, where did you learn that ^_^

hexem

If you wanted to enable portfast and bpdguard on more than one interface at a time you would use the range command.

interface range fa0/1 - 24

Now you get a subconfig mode for all 24 ports.

notgoing2fail

mgeorge wrote: »

I'm curious, where did you learn that ^_^

I just jumped on my switch and played with the commands.

mgeorge

notgoing2fail wrote: »

I just jumped on my switch and played with the commands.

Ahhh, I was just wondering because two days ago I published lab 4-17 which goes over that;

Configuring Switchport Spanning Tree BPDU Guard | Free CCNA Workbook

notgoing2fail

mgeorge wrote: »

Ahhh, I was just wondering because two days ago I published lab 4-17 which goes over that;

Configuring Switchport Spanning Tree BPDU Guard | Free CCNA Workbook

Good stuff!

You know another thing that is kinda funny is I played with turning off spanning-tree.

no spanning-tree

But there's no enable spanning-tree. I think the only option is:

spanning-tree mode pvst

I suppose that command puts you back in 802.1D ? Because the other option is for rapid-pvst and mst.

I would have thought that there would be a default enable command such as:

spanning-tree enable

That would default to 802.1D...

Cisco is kinda funny sometimes with their commands.....