User`s manual

User’s Manual 347
configuration message) becomes the designated port for the attached LAN. If it is a root port, a new root port
is selected from among the device ports attached to the network.
Example
The following is sample output from the spanning-tree max-age command.
Console(config)#spanning-tree max-age 40
Console(config)#
16.220 spanning-tree mode
This command selects the spanning tree mode for this switch. Use the no form to restore the default.
Syntax Description
spanning-tree mode {stp | rstp | mstp}
no spanning-tree mode
stp Spanning Tree Protocol (IEEE 802.1D)
rstp Rapid Spanning Tree Protocol (IEEE 802.1w)
mstp Multiple Spanning Tree (IEEE 802.1s)
Default
mstp
Command Mode
Global Configuration
Usage Guidelines
Spanning Tree Protocol
• Uses RSTP for the internal state machine, but sends only 802.1D BPDUs.
This creates one spanning tree instance for the entire network. If multiple VLANs are implemented on a
network, the path between specific VLAN members may be inadvertently disabled to prevent network loops,
which isolates group members. To presvent this select the MSTP option operating multiple VLANs.
Rapid Spanning Tree Protocol
RSTP supports connections to either STP or RSTP nodes by monitoring the incoming protocol messages
and dynamically adjusting the type of protocol messages, the RSTP node transmits, as described below:
• STP Mode – If the switch receives an 802.1D BPDU after a port’s migration delay timer expires, the
switch assumes it is connected to an 802.1D bridge and starts using only 802.1D BPDUs.
• RSTP Mode – If RSTP is using 802.1D BPDUs on a port and receives an RSTP BPDU after the
migration delay expires, RSTP restarts the migration delay timer and begins using RSTP BPDUs on
that port.