Brocade FastIron Ethernet Switch Platform and Layer 2 Switching Configuration Guide - Manual (Page 269)

NOTE
When the wiring closet switch (Brocade device) first comes up or when STP is first enabled, the uplink
ports still must go through the standard STP state transition without any acceleration. This behavior
guards against temporary routing loops as the switch tries to determine the states for all the ports. Fast
Uplink Span acceleration applies only when a working uplink becomes unavailable.
Active uplink port failure
The active uplink port is the port elected as the root port using the standard STP rules. All other ports in
the group are redundant uplink ports. If an active uplink port becomes unavailable, Fast Uplink Span
transitions the forwarding of traffic to one of the redundant ports in the Fast Uplink Span group in one
second bypassing listening and learning port states.
Switchover to the active uplink port
When a failed active uplink port becomes available again, switchover from the redundant port to the
active uplink port is delayed by 30 seconds. The delay allows the remote port to transition to forwarding
mode using the standard STP rules. After 30 seconds, the blocked active uplink port begins forwarding
in just one second and the redundant port is blocked.
NOTE
Use caution when changing the spanning tree priority. If the switch becomes the root bridge, Fast
Uplink Span will be disabled automatically.
Fast Uplink Span Rules for Trunk Groups
If you add a port to a Fast Uplink Span group that is a member of a trunk group, the following rules
apply:
• If you add the primary port of a trunk group to the Fast Uplink Span group, all other ports in the trunk
group are automatically included in the group. Similarly, if you remove the primary port in a trunk
group from the Fast Uplink Span group, the other ports in the trunk group are automatically 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 ports in 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 the backup
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 an accelerated
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. The
accelerated transition applies to all ports in this trunk group.
When the original working trunk group comes back (partially or fully), the transition back to the original
topology is accelerated if the conditions listed above are met.
Active uplink port failure
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