BigIron RX Series Configuration Guide 38153-1001810-01Configuring RSTP parameters 13Fast uplink spanThe Fast Port Span feature described in the previous section enhances STP performance for endstations. The Fast Uplink feature enhances STP performance for wiring closet switches withredundant uplinks. Using the default value for the standard STP forward delay, convergencefollowing a transition from an active link to a redundant link can take 30 seconds (15 seconds forlistening and an additional 15 seconds for learning).You can use the Fast Uplink feature on a Brocade device deployed as a wiring closet switch todecrease the convergence time for the uplink ports to another device to just four seconds (twoseconds for listening and two seconds for learning). The wiring closet switch must be a Brocadedevice but the device at the other end of the link can be a Brocade device or another vendor’sswitch. Configuration of the Fast Uplink Span feature takes place entirely on the Brocade device.To configure the Fast Uplink Span feature, specify a group of ports that have redundant uplinks onthe wiring closet switch (Brocade device) as members of a Fast Uplink Group. If the active linkbecomes unavailable, the Fast Uplink Span feature transitions the forwarding to one of the otherports in four seconds. You can configure one Fast Uplink Span group on the device. All Fast UplinkSpan ports are members of the same Fast Uplink Span group.NOTETo avoid the potential for temporary bridging loops, Brocade recommends that you use the FastUplink feature only for wiring closet switches (switches at the edge of the network cloud). Inaddition, enable the feature only on a group of ports intended for redundancy, so that at any giventime only one of the ports is expected to be in the forwarding state.NOTEWhen the BigIron RX first comes up or when STP is first enabled, the uplink ports still must gothrough the standard STP state transition without any acceleration. This behavior guards againsttemporary routing loops as the switch tries to determine the states for all the ports. Fast Uplink Spanacceleration applies only when a working uplink becomes unavailable.Fast uplink span rules for trunk groupsIf you add a port to a Fast Uplink Span group that is a member of a trunk group, the following rulesapply:• If you add the primary port of a trunk group to the Fast Uplink Span group, all other ports in thetrunk group are automatically included in the group. Similarly, if you remove the primary port ina trunk group from the Fast Uplink Span group, the other ports in the trunk group areautomatically removed from the Fast Uplink Span group.• You cannot add a subset of the ports in a trunk group to the Fast Uplink Span group. All portsin a trunk group have the same Fast Uplink Span property, as they do for other port properties.• If the working trunk group is partially down but not completely down, no switch-over to thebackup occurs. This behavior is the same as in the standard STP feature.• If the working trunk group is completely down, a backup trunk group can go through anaccelerated transition only if the following are true:• The trunk group is included in the fast uplink group.• All other ports except those in this trunk group are either disabled or blocked. Theaccelerated transition applies to all ports in this trunk group.
