Foundry Networks Switch and Router Installation And Configuration Manual page 382

Foundry Switch and Router Installation and Configuration Guide
NOTE: This feature applies only to Chassis and TurboIron/8 Layer 2 Switches and Layer 3 Switches.
NOTE: If you are considering enabling single STP on the Foundry device in order to interoperate with Cisco
devices that are running PVST/PVST+, use PVST or PVST+ on the Cisco devices and use Foundry's PVST
support instead. The PVST/PVST+ support is automatically enabled in PVST/PVST+ environments and does not
require any configuration changes. Using PVST+ and enabling single STP on the Foundry device can require
STP configuration changes and is less flexible for load balancing using STP.
STP Defaults
STP is enabled by default on switches and disabled by default on Layer 3 Switches. On Layer 2 and Layer 3
Switches, each port-based VLAN runs a separate instance of STP by default. Thus, on devices that have multiple
port-based VLANs, each VLAN has its own spanning tree domain. In addition, the STP state of each port-based
VLAN is independent of the STP states of other VLANs. You can have STP enabled on port-based VLAN 10, but
disabled on port-based VLANs 20 and 30, and so on.
When you configure a port-based VLAN, that VLAN inherits the STP state of the default port-based VLAN. Thus,
if STP is enabled on the default VLAN, STP is also enabled on the new port-based VLAN. You can change the
STP state of the VLAN afterwards. Changes to the STP state of the default VLAN do not affect existing VLANs. A
change to the STP state affects only the VLANs you create after the change.
Single STP and Existing Port-Based VLANs
When you enable single STP, all the ports that are in port-based VLANs with STP enabled become members of a
single spanning tree domain. Thus, the ports share a single BPDU broadcast domain. The Foundry device
places all the ports in a non-configurable VLAN, 4094, to implement the single STP domain. However, this VLAN
does not affect port membership in the port-based VLANs you have configured. Other broadcast traffic is still
contained within the individual port-based VLANs. Therefore, you can use single STP while still using your
existing VLAN configurations without changing your network. In addition, single STP does not affect 802.1q
tagging. Tagged and untagged ports alike can be members of the single spanning tree domain.
NOTE: When single STP is enabled, the BPDUs on tagged ports go out untagged.
If STP is disabled on a VLAN when you enable single STP, STP remains disabled on the ports in that VLAN and
that VLAN does not become a member of the single STP domain. To enable STP on the VLAN, you must first
disable single STP, enable STP on the VLAN, then re-enable single STP.
Enabling Single STP
To enable single STP, use one of the following methods.
NOTE: If the device has only one port-based VLAN (the default VLAN), then the device is already running a
single instance of STP. In this case, you do not need to enable single STP. You need to enable single STP only if
the device contains more than one port-based VLAN and you want all the ports to be in the same STP broadcast
domain.
USING THE CLI
To configure the Foundry device to run a single spanning tree, enter the following command at the global CONFIG
level.
BigIron(config) spanning-tree single
Here is the syntax for the global STP parameters.
Syntax: [no] spanning-tree single [forward-delay <value>]
[hello-time <value>] | [maximum-age <time>] | [priority <value>]
Here is the syntax for the STP port parameters.
Syntax: [no] spanning-tree single [ethernet <portnum> path-cost <value> | priority <value>]
12 - 20 December 2000