Configuration Guide User guide

1112 FastIron Configuration Guide
53-1002494-02
STP feature configuration
Similarly Switch 3 has a bridge priority value inferior to Switch 2. Port3 on Switch 3 connects to Port
3 on Switch 2. This port will be given the Alternate port role, since a Root port is already established
on this bridge.
Assignment of ports on Switch 4
Switch 4 is not directly connected to the root bridge. It has two ports with superior incoming RST
BPDUs from two separate LANs: Port3 and Port4. The RST BPDUs received on Port3 are superior to
the RST BPDUs received on port 4; therefore, Port3 becomes the Root port and Port4 becomes the
Alternate port.
Edge ports and edge port roles
The Brocade implementation of 802.1W allows ports that are configured as Edge ports to be
present in an 802.1W topology. (Figure 127). Edge ports are ports of a bridge that connect to
workstations or computers. Edge ports do not register any incoming BPDU activities.
Edge ports assume Designated port roles. Port flapping does not cause any topology change
events on Edge ports since 802.1W does not consider Edge ports in the spanning tree calculations.
FIGURE 127 Topology with edge ports
However, if any incoming RST BPDU is received from a previously configured Edge port, 802.1W
automatically makes the port as a non-edge port. This is extremely important to ensure a loop free
Layer 2 operation since a non-edge port is part of the active RSTP topology.
Switch 1
Bridge priority = 600
Switch 2
Bridge priority = 1000
Switch 3
Bridge priority = 2000
Port2 Port2
Port3
Port3
Port3
Port2
Port5
Edge Port
Port5
Edge Port