Configuration Guide User guide

FastIron Configuration Guide 1113
53-1002494-02
STP feature configuration
The 802.1W protocol can auto-detect an Edge port and a non-edge port. An administrator can also
configure a port to be an Edge port using the CLI. It is recommended that Edge ports are
configured explicitly to take advantage of the Edge port feature, instead of allowing the protocol to
auto-detect them.
Point-to-point ports
To take advantage of the 802.1W features, ports on an 802.1W topology should be explicitly
configured as point-to-point links using the CLI. Shared media should not be configured as
point-to-point links.
NOTE
Configuring shared media or non-point-to-point links as point-to-point links could lead to Layer 2
loops.
The topology in Figure 128 is an example of shared media that should not be configured as
point-to-point links. In Figure 128, a port on a bridge communicates or is connected to at least two
ports.
FIGURE 128 Example of shared media
Bridge port states
Ports 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 or
VLAN can reach the root bridge using another port, whose state is forwarding. When a port is
in this state, the port does not transmit or receive data frames, but the port does continue to
receive 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 not
permit forwarding of data frames. The device can learn the MAC addresses of frames that the
port 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 is
disconnected 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 port
on that bridge assumes the Root port role, then the old Root port moves into a discarding state as
it assumes another port role.