Brocade Multi-Service IronWare Switching Configuration Guide (Supporting R05.6.00) - Manual (Page 364)

334 Multi-Service IronWare Switching Configuration Guide
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IEEE Single Spanning Tree (SSTP)
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IEEE Single Spanning Tree (SSTP)
By default, each port-based VLAN on the Brocade device runs a separate spanning tree, which you
can enable or disable on an individual VLAN basis.
Alternatively, you can configure the Brocade device to run a single spanning tree across all of its
ports and VLANs. The SSTP feature is especially useful for connecting a Brocade device to
third-party devices that run a single spanning tree in accordance with the 802.1q specification.
SSTP uses the same parameters, with the same value ranges and defaults, as the default STP
supported on the Brocade device. Refer to
“Default STP bridge and port parameters” .
SSTP defaults
SSTP is disabled by default. When you enable the feature, all VLANs on which STP is enabled
become members of a single spanning tree. All VLANs on which STP is disabled are excluded from
the single spanning tree:
• To add a VLAN to the single spanning tree, enable STP on that VLAN.
• To remove a VLAN from the single spanning tree, disable STP on that VLAN.
When you enable SSTP, 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 Brocade device places all the ports in a non-configurable VLAN, 4095, to implement
the SSTP 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 SSTP while still using your existing VLAN configurations without
changing your network. In addition, SSTP does not affect 802.1q tagging. Tagged and untagged
ports alike can be members of the single spanning tree domain.
NOTE
When SSTP is enabled, the BPDUs on tagged ports go out untagged.
If you disable SSTP, all VLANs that were members of the single spanning tree now do not run any
form of spanning tree. Per VLAN STP can be enabled again using either global STP enable or the
spanning-tree enable command under individual VLANs.
NOTE
If the Brocade device has only one port-based VLAN (the default VLAN), then it is already running a
single instance of STP. In this case, you do not need to enable SSTP. You need to enable SSTP only
if the Brocade device contains more than one port-based VLAN and you want all the ports to be in
the same STP broadcast domain.
To configure the Brocade device to run a single spanning tree, enter the following command at the
global CONFIG level.
Brocade(config)# spanning-tree single
To change a global STP parameter, enter a command such as the following at the global CONFIG
level.
Brocade(config) spanning-tree single priority 2
This command changes the STP priority for all ports to 2.