URGNT - STP question 1

[imbadatthis]

sitting in a class - im pretty sure instructor is wrong.. but i need proof before i open my big mouth ..

talking about stp ...

he has 4 switches on the board, full mesh .
he is suggesting that when Switch with the lowest Mac address ( assumption is default priority) loses ONE link to another switch, then STP root becomes the second switch with the lowest mac address (ie the designated switch ) .

my understanding was that if the actuall root goes down, ie no more root bpdu's are recieved by the network, THEN the DR kicks in, ie: someone reloads root
can u please advise.

thanks,

 

[North323]

he may have to qualify that statment. what is the priority of the other switch:

Select a root bridge. The root bridge of the spanning tree is the bridge with the smallest (lowest) bridge ID. Each bridge has a unique identifier (ID) and a configurable priority number; the bridge ID contains both numbers. To compare two bridge IDs, the priority is compared first. If two bridges have equal priority, then the MAC addresses are compared. For example, if switches A (MAC=0200.0000.1111) and B (MAC=0200.0000.2222) both have a priority of 10, then switch A will be selected as the root bridge. If the network administrator would like switch B to become the root bridge, they must set its priority to be less than 10.

 

[unclerico]

if the root bridge is still reachable via other links then all that will happen is one of the designated ports (or blocking ports depending on how everything ends up in the topology) will transition to the root port. Only when the root becomes completely isolated will the secondary root take over. And remember, if you don't design the STP topology correct from teh beginning by manually designating a root and secondary root bridge you could be in for a world of hurt.

I hate all Uppercase... I don't want my groups to seem angry at me all the time! =)
- ColdFlame (vbscript forum)

 

[imbadatthis]

unclerico,

i agree, hence me posting this, is there a link, i looked quickly online, while i was in class - ....

Im studying for my ccnp , and i knew this guy was high on something when he said that the switch would stop being the root switch.. i tried to argue with him AFTER class was over ... but he kept insisting that the switch will give up being root, even though it was elected as such, and no other thing except ONE link going down..

so if you have a link, it would be awesome!!!!
thanks,

 

[unclerico]

it's the basics of STP my man. So each bridge will send BPDU's. Each bridge will assume that they are root upon connection. They determine which bridge is root by either the lowest mac address or by the administrator manually configuring the bridge priority for each VLAN. When BPDU's are exchanged between switches, the switches will make the determination of the root bridge depening on whether or not they receive superior BPDU's. Once the root bridge is agreed upon, each switch will identify its root port (the port with the shortest path to the root). They will then identify their designated ports and their alternate/blocking ports (if any). Every two seconds by default BPDU's are exchanged between switches. The BPDU's are also received on blocking ports, but because these BPDU's are inferior the port never transitions to forwarding/root. In the event that the current root port is isolated from the root bridge (either by link failure or admin shutdown) the blocking port is still receiving BPDU's from the root. Since the current root port is no longer receiving BPDU's the current blocking port will wait 2x forwarding delay and transition to forwarding and become the root port. The key is that the root bridge is still alive and the downlevel switch is still able to receive the BPDU's. The secondary root will only become root if the primary is completely isolated.

Have your instructor lab it up and see for himself. If he doesn't want to I can and I will post the results.

I hate all Uppercase... I don't want my groups to seem angry at me all the time! =)
- ColdFlame (vbscript forum)

 

[burtsbees]

Is there only one link in your instructor's example by chance?

/

tim@tim-laptop ~ $ sudo apt-get install windows
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Couldn't find package windows...Thank Goodness!