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Enhancements in Release F.02.11
Fast-Uplink Spanning Tree Protocol (STP)
Operating Rules for Fast Uplink
■ A switch with ports configured for fast uplink must be an edge switch and not either an
interior switch or the STP root switch.
Configure fast-uplink on only the edge switch ports used for providing redundant STP uplink
connections in a network. (Configuring Fast-Uplink STP on ports in interior switches can create
network performance problems.) That is, a port configured for STP uplink should not be
connected to a switch that is sequentially further away from the STP root device. For example,
switch "4" in figure 68 (page 150) is an edge switch.
■ Configure fast uplink on a group (two or more) of redundant edge-switch uplink ports where
only one port in the group is expected to be in the forwarding state at any given time.
■ Edge switches cannot be directly linked together using fast-uplink ports. For example, the
connection between switches 4 and 5 in figure 69 is not allowed for fast-uplink operation.
Figure 69. Example of a Disallowed Connection Between Edge Switches
■ Apply fast-uplink only on the uplink ports of an edge switch. For example, on switch "4" (an
edge switch) in figure 69 above, only the ports connecting switch "4" to switches "2" and "3"
are upstream ports that would use fast uplink. Note also that fast uplink should not be
configured on both ends of a point-to-point link, but only on the uplink port of an edge switch.
■ Ensure that the switch you intend as a backup root device will in fact become the root if the
primary root fails, and that no ports on the backup root device are configured for fast-uplink
operation. For example, if the
STP Priority is the same on all switches—default: 32768—then
the switch with the lowest MAC address will become the root switch. If that switch fails,
then the switch with the next-lowest MAC address will become the root switch. Thus, you
can use
STP Priority to control which switch STP selects as the root switch and which switch
will become the root if the first switch fails.
■ Fast-Uplink STP requires a minimum of two uplink ports.
Switch 4
(2512-Edge)
Switch 3
Switch 1
(Root)
Switch 2
Link blocked by STP:
LAN
Switch 5
(2524-Edge)
The ports that
make up this
link cannot be
configured as
fast-uplink
ports.