C P P C L R; Stp Parameters And Defaults - Foundry Networks Switch and Router Installation And Configuration Manual

Foundry Switch and Router Installation and Configuration Guide

STP Parameters and Defaults

Table 12.1 lists the default STP bridge parameters. The bridge parameters affect the entire VLAN (or the entire
device, if the only port-based VLAN is the default one, VLAN 1).
Parameter Description
Forward Delay The period of time a bridge will wait (the listen and learn
period) before beginning to forward data packets.
Maximum Age The interval a bridge will wait for a hello packet from the
root bridge before initiating a topology change.
Hello Time The interval of time between each configuration BPDU
sent by the root bridge.
Priority A parameter used to identify the root bridge in a
spanning tree (instance of STP). The bridge with the
lowest value has the highest priority and is the root.
A higher numerical value means a lower priority; thus,
the highest priority is 0.
Table 12.2 lists the default STP port parameters. The port parameters affect individual ports and are separately
configurable on each port.
Parameter Description
Priority The preference that STP gives this port relative to other
ports for forwarding traffic out of the spanning tree.
A higher numerical value means a lower priority; thus,
the highest priority is 0.
Path Cost The cost of using the port to reach the root bridge. When
selecting among multiple links to the root bridge, STP
chooses the link with the lowest path cost and blocks the
other paths. Each port type has its own default STP path
cost.
Notice that the path costs favor 100 Mbps and faster Ethernet ports over Packet over SONET (POS) ports. STP
applies to POS ports only when they are configured for Layer 2 switching. The POS paths are remote (WAN)
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Table 12.1: Default STP Bridge Parameters
Table 12.2: Default STP Port Parameters
Default and Valid Values
15 seconds
Possible values: 4 – 30
seconds
20 seconds
Possible values: 6 – 40
seconds
2 seconds
Possible values: 1 – 10
seconds
32768
Possible values: 0 – 65535
Default and Valid Values
128
Possible values: 0 – 255
10 Mbps – 100
100 Mbps – 19
Gigabit – 4
OC-3c – 200
OC-12c – 80
OC-48c – 20
Possible values are 0 –
65535
December 2000