Cisco 3845 - Security Bundle Router Software Guide

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Cisco ME 3800X and 3600X Switch Software Configuration Guide
OL-23400-01
Chapter 13 Configuring STP
Configuring Spanning-Tree Features
• Configuring a Secondary Root Switch, page 13-15 (optional)
• Configuring Port Priority, page 13-16 (optional)
• Configuring Path Cost, page 13-18 (optional)
• Configuring the Switch Priority of a VLAN, page 13-19 (optional)
• Configuring Spanning-Tree Timers, page 13-20 (optional)
Default Spanning-Tree Configuration
Table 13-3 shows the default spanning-tree configuration.
Spanning-Tree Configuration Guidelines
If more VLANs are defined than there are spanning-tree instances, you can enable PVST+ or rapid
PVST+ on STP ports s in only 128 VLANs on the switch. The remaining VLANs operate with spanning
tree disabled. However, you can map multiple VLANs to the same spanning-tree instances by using
MSTP. For more information, see Chapter 14, “Configuring MSTP.”
If 128 instances of spanning tree are already in use, you can disable spanning tree on STP ports in one
of the VLANs and then enable it on the VLAN where you want it to run. Use the no spanning-tree vlan
vlan-id global configuration command to disable spanning tree on a specific VLAN, and use the
spanning-tree vlan vlan-id global configuration command to enable spanning tree on the desired
VLAN.
Table 13-3 Default Spanning-Tree Configuration
Feature Default Setting
Enable state Enabled on ports in VLAN 1.
Spanning-tree mode Rapid PVST+
Rapid PVST+ interoperates with PVST and PVST+.
MSTP is disabled.
Switch priority 32768.
Spanning-tree port priority (configurable on a per-interface basis) 128.
Spanning-tree port cost (configurable on a per-interface basis) 1000 Mbps: 4.
100 Mbps: 19.
10 Mbps: 100.
Spanning-tree VLAN port priority (configurable on a per-VLAN
basis)
128.
Spanning-tree VLAN port cost (configurable on a per-VLAN
basis)
1000 Mbps: 4.
100 Mbps: 19.
10 Mbps: 100.
Spanning-tree timers Hello time: 2 seconds.
Forward-delay time: 15 seconds.
Maximum-aging time: 20 seconds.

Cisco 3845 - Security Bundle Router Specifications

General

Brand	Cisco
Model	3845 - Security Bundle Router
Category	Switch
Language	English