Spanning Tree protocol: port state related question

[sixth_sense]

Hi all,

I came to know a noon root switch in spanning tree protocol environment can have only one designated port. (a designated prot stay in forwarding state- which can forward frame) -- If so,what about other ports that are directly connected to pc/terminals?

which mode they are on?

[Georg Pauwen]

Hello,

the concept of root and designated ports has significance only for connections between switches. User ports, where PCs and terminals are directly connected, have no up or downlink to other switches and should actually not even participate in the spanning-tree algorithm (which is usually accomplished with the 'spanning-tree portfast' interface command, for IOS).

HTH,

GP

[sixth_sense]

Ok, thanks for the reply. now i understand.

but there is a new question in my mind...whats the difference between a root port and a designated port?

[Georg Pauwen]

Hello,

let's say you have three switches, SwitchA, SwitchB, and SwitchC. SwitchA is the root bridge, here is what the root ports (RP) and the designated ports (DP) would look like:

SwitchA (DP) --> (RP) SwitchB (DP) --> (RP) SwitchC

The concept is that the port leading TO the root switch is the root port, and the port leading away from the switch to another switch is the designated port. That also means that the root switch itself does not have any root, but only designated ports.

Does that make sense ?

Regards,

GP

[sixth_sense]

I got this:

"A designated port is the connection used to send and receive packets on a SPECIFIC SEGMENT."

from this site:

http://computer.howstuffworks.com/lan-switch14.htm

So, isn't a root port of any (non-root bridge) also a designated port - for the sigment connected towards root bridge?

Thanks,

[Richard Burts]

This response says that with portfast the port does not participate in the Spanning Tree. This is not correct. The port does still participate in the Spanning Tree when configured with portfast (as I have demonstrated a few times when I connected something to a port with portfast which did in fact create a loop). What portfast does is bypass the listening state and the learning state and go directly to the forwarding state. But BPDUs are being sent and a loop will be detected.