360 BigIron RX Series Configuration Guide53-1002253-01Edge ports and edge port roles13Ports Switch 4Switch 4 is not directly connected to the root bridge. It has two ports with superior incoming RSTBPDUs from two separate LANs: Port3 and Port4. The RST BPDUs received on Port3 are superior tothe RST BPDUs received on port 4; therefore, Port3 becomes the Root port and Port4 becomes theAlternate port.Edge ports and edge port rolesBrocade’s implementation of RSTP allows ports that are configured as Edge ports to be present inan RSTP topology. (Figure 41). Edge ports are ports of a bridge that connect to workstations orcomputers. Edge ports do not register any incoming BPDU activities.Edge ports assume Designated port roles. Port flapping does not cause any topology changeevents on Edge ports since RSTP does not consider Edge ports in the spanning tree calculations.FIGURE 41 Topology with edge portsHowever, if any incoming RST BPDU is received from a previously configured Edge port, RSTPautomatically makes the port as a non-edge port. This is extremely important to ensure a loop freeLayer 2 operation since a non-edge port is part of the active RSTP topology.The bridge detection state module can auto-detect an Edge port and a non-edge port. Anadministrator can also configure a port to be an Edge port. It is recommended that Edge ports areconfigured explicitly to take advantage of the Edge port feature, instead of allowing the protocol toauto-detect them.Switch 1Bridge priority = 600 Switch 2Bridge priority = 1000Switch 3Bridge priority = 2000Port2 Port2Port3 Port3Port3Port2Port5Edge PortPort5Edge Port
