Reference Guide

Spanning Tree Protocol | 695
STP Root Selection
The Spanning Tree Protocol determines the root bridge, but you can assign one bridge a lower priority to
increase the likelihood that it will be selected as the root bridge. You can also specify that a bridge is the
root or the secondary root.
To change the bridge priority or specify that a bridge is the root or secondary root:
View only the root information using the
show spanning-tree root command (see Figure 38-9) from EXEC
privilege mode.
Figure 38-9. show spanning-tree root Command Example
SNMP Traps for Root Elections and Topology Changes
• Enable SNMP traps for Spanning Tree state changes using the command snmp-server enable traps stp.
• Enable SNMP traps for RSTP, MSTP, and PVST+ collectively using the command
snmp-server enable
traps xstp.
Configuring Spanning Trees as Hitless
Configuring Spanning Trees as Hitless is supported only on platforms: c e
You can configure Spanning Tree (STP), Rapid Spanning Tree (RSTP), Multiple Spanning Tree (MSTP),
and Per-Vlan Spanning Tree (PVST+) to be hitless (all or none must be configured as hitless). When
configured as hitless, critical protocol state information is synchronized between RPMs so that RPM
failover is seamless, and no topology change is triggered.
Configure all Spanning Tree types to be hitless using the command
redundancy protocol xstp from
CONFIGURATION mode, as shown in Figure 38-10.
Task Command Syntax Command Mode
Assign a number as the bridge priority or designate it as the
root or secondary root.
priority-value range: 0 to 65535. The lower the number
assigned, the more likely this bridge will become the root
bridge. The default is 32768.
• The primary option specifies a bridge priority of 8192.
• The secondary option specifies a bridge priority of 16384.
bridge-priority {priority-value |
primary | secondary}
PROTOCOL
SPANNING TREE
FTOS#show spanning-tree 0 root
Root ID Priority 32768, Address 0001.e80d.2462
We are the root of the spanning tree
Root Bridge hello time 2, max age 20, forward delay 15
FTOS#