Product guide

Spanning-Tree Operation
802.1D Spanning-Tree Protocol (STP) on 5300xl, 3400cl and 6400cl Switches
to transition to forwarding. In a normal spanning tree environment, this
transition is usually 30 seconds (with the
Forward Delay parameter set to its
default of 15 seconds). However, by using the fast-uplink spanning tree
feature, a port on a switch used as an edge switch can make this transition in
as little as ten seconds. (In an STP environment, an edge switch is a switch
that is connected only to switches that are closer to the STP root switch than
the edge switch itself, as shown by switch “4” in figure 6-13, below.)
Switch 4
(4108-Edge)
Switch 3
Switch 1
(Root)
Switch 2
Port 3
Port 5
Link blocked by STP:
1
6
8
LAN
Figure 6-13. Example of an Edge Switch in a Topology Configured for STP Fast Uplink
In figure 6-13, STP is enabled and in its default configuration on all switches,
unless otherwise indicated in table 6-5, below:
Table 6-5. STP Parameter Settings for Figure 6-13
STP Parameter Switch “1” Switch “2” Switch “3” Switch “4”
Switch Priority 0
1
1
2
32,768 (default) 32,768 (default)
(Fast) Uplink No No No Ports 3 & 5
1
This setting ensures that Switch “1” will be the primary root switch for STP in figure 6-13.
2
This setting ensures that Switch “2” will be the backup root switch for STP in figure 6-13.
With the above-indicated topology and configuration:
■ Scenario 1: If the link between switches “4” and “2” goes down, then the
link between switches “4” and “3” will begin forwarding in as little as ten
seconds.
■ Scenario 2: If Switch “1” fails, then:
• Switch “2” becomes the root switch.
• The link between Switch “3” and Switch “2” begins forwarding.
• The link between Switch “2” and the LAN begins forwarding.
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.
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