232 PowerConnect B-Series FCX Configuration Guide53-1002266-01Configuring STP related features8NOTEConfiguring shared media or non-point-to-point links as point-to-point links could lead to Layer 2loops.The topology in Figure 28 is an example of shared media that should not be configured aspoint-to-point links. In Figure 28, a port on a bridge communicates or is connected to at least twoports.FIGURE 28 Example of shared mediaBridge port statesPorts roles can have one of the following states:• Forwarding – 802.1W is allowing the port to send and receive all packets.• Discarding – 802.1W has blocked data traffic on this port to prevent a loop. The device orVLAN can reach the root bridge using another port, whose state is forwarding. When a port isin this state, the port does not transmit or receive data frames, but the port does continue toreceive RST BPDUs. This state corresponds to the listening and blocking states of 802.1D.• Learning – 802.1W is allowing MAC entries to be added to the filtering database but does notpermit forwarding of data frames. The device can learn the MAC addresses of frames that theport receives during this state and make corresponding entries in the MAC table.• Disabled – The port is not participating in 802.1W. This can occur when the port isdisconnected or 802.1W is administratively disabled on the port.A port on a non-root bridge with the role of Root port is always in a forwarding state. If another porton that bridge assumes the Root port role, then the old Root port moves into a discarding state asit assumes another port role.A port on a non-root bridge with a Designated role starts in the discarding state. When that portbecomes elected to the Root port role, 802.1W quickly places it into a forwarding state. However, ifthe Designated port is an Edge port, then the port starts and stays in a forwarding state and itcannot be elected as a Root port.A port with an Alternate or Backup role is always in a discarding state. If the port role changes toDesignated, then the port changes into a forwarding state.If a port on one bridge has a Designated role and that port is connected to a port on another bridgethat has an Alternate or Backup role, the port with a Designated role cannot be given a Root portrole until two instances of the forward delay timer expires on that port.
