Dell PowerConnect B-FCXs, Configuration Manual

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208 PowerConnect B-Series FCX Configuration Guide
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Configuring standard STP parameters
8
Configuring standard STP parameters
Layer 2 Switches and Layer 3 Switches support standard STP as described in the IEEE 802.1D
specification. STP is enabled by default on Layer 2 Switches but disabled by default on Layer 3
Switches.
By default, each port-based VLAN on a Dell PowerConnect device runs a separate spanning tree (a
separate instance of STP). A Dell PowerConnect device has one port-based VLAN (VLAN 1) by
default that contains all the device ports. Thus, by default each Dell PowerConnect device has one
spanning tree. However, if you configure additional port-based VLANs on a Dell PowerConnect
device, then each of those VLANs on which STP is enabled and VLAN 1 all run separate spanning
trees.
If you configure a port-based VLAN on the device, the VLAN has the same STP state as the default
STP state on the device. Thus, on Layer 2 Switches, new VLANs have STP enabled by default. On
Layer 3 Switches, new VLANs have STP disabled by default. You can enable or disable STP in each
VLAN separately. In addition, you can enable or disable STP on individual ports.
STP parameters and defaults
Table 47 lists the default STP states for Dell PowerConnect devices.
Table 48 lists the default STP bridge parameters. The bridge parameters affect the entire spanning
tree. If you are using MSTP, the parameters affect the VLAN. If you are using SSTP, the parameters
affect all VLANs that are members of the single spanning tree.
TABLE 47
Default STP states
Device type Default STP type Default STP state Default STP state of new
VLANs
1
1. When you create a port-based VLAN, the new VLAN STP state is the same as the default STP state on the
device. The new VLAN does not inherit the STP state of the default VLAN.
Layer 2 Switch MSTP
2
2. MSTP stands for “Multiple Spanning Tree Protocol”. In this type of STP, each port-based VLAN, including the
default VLAN, has its own spanning tree. References in this documentation to “STP” apply to MSTP. The Single
Spanning Tree Protocol (SSTP) is another type of STP. SSTP includes all VLANs on which STP is enabled in a single
spanning tree. Refer to
“Single Spanning Tree (SSTP)” on page 269.
Enabled Enabled
Layer 3 Switch MSTP Disabled Disabled
TABLE 48 Default STP bridge parameters
Parameter Description Default and valid values
Forward Delay The period of time spent by a port in the listening and
learning state before moving on to the learning or
forwarding state, respectively.
The forward delay value is also used for the age time of
dynamic entries in the filtering database, when a topology
change occurs. 15 seconds
Possible values: 4 – 30
seconds
Maximum Age The interval a bridge will wait for a configuration BPDU
from the root bridge before initiating a topology change. 20 seconds
Possible values: 6 – 40
seconds