spanning tree protocol

agha

Can anybody explain me how does Spanning Tree Protocol work? ( with graphics please )

In the class i understood but, when go back and check my notes i confused.

thank you very much in advance.

AceAll

This link should help you in understanding the spaning tree protocol

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat5000/rel_4_4/config/spantree.htm[/url]

agha

thanks fo the answer but its so hard something simple
i need.

AceAll

You can refer Wendell Odom's ICND book. I feel the spaning tree protocol has been explained in lucid manner over there.

Hulkamaniac

Lammle's sybex 5th edition goes over stp in an even easier manner.

agha

thanks for your help!
can anybody answer this spesific question?

`The bridges elect a root bridge based on the bridge IDs in the BPDUs.The root bridge is the bridge with the lowest numeric value for the bridge ID. Because the two-part bridge ID starts with priority value, essentially the bridge with lowest priority becomes root.`

in this sentence what is the `priority value`?

I tried to findan explanation about priority value but I couldnt. CAn anyone tell me how can we calculate, or assign this value?

darkuser

hth

www.cisco.com/univercd/cc/td/doc/product/rtrmgmt/sw_ntman/cwsimain/cwsi2/cwsiug2/vlan2/stpapp.htm

www.cisco.com/univercd/cc/td/doc/product/lan/cat5000/rel_5_2/config/spantree.htm

agha

But I understood nothing here.

AL i want to lear is it defaoult value, if it is , how is it calculated?
I know now we change it, assign new one.

elcaminoguy

I think I now know where I messed up on one question on my CCNA exam today and it has to do with this topic. If all switches have the default priority of 32768 then the fallback for election of the root switch will use the lowest MAC address to decide which switch is root. Apparently it doesn't care about speed of ports or even the model of the switch. As in 2950G versus 1900 series. You can rig that election by changing the priority value of the switch to overcome the default election rules for STP This quoute from the link says the same thing..

"The switch with the highest bridge priority (the lowest numerical priority value) is elected as the root switch. If all switches are configured with the default priority (3276, the switch with the lowest MAC address in the Layer 2 network becomes the root switch."

Also this link spells it out too.
http://www.cisco.com/warp/public/473/5.html

So you can rig the election and force the switch to be root by setting the set spantree root command vlan id

so to get your switch to be root for STP on vlan 1 issue the command

set spantree root 1

...If I'm wrong about this please someone let me know.

If I'm right then glad to help, If I'm wrong, sorry for the added confusion.