BigIron RX Series Configuration Guide 341
53-1002253-01
IEEE Single Spanning Tree (SSTP)
12
SSTP uses the same parameters, with the same value ranges and defaults, as the default STP
supported on the device. Refer to “Default STP bridge and port parameters” on page 328.
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 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.
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 run MSTP instead. In
MSTP, each VLAN has its own spanning tree. VLANs that were not members of the single spanning
tree were not enabled for STP. Therefore, STP remains disabled on those VLANs.
Enabling SSTP
If the 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
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 device to run a single spanning tree, enter the following command at the global
CONFIG level.
BigIron RX(config)# spanning-tree single
If the device has only one port-based VLAN, the CLI command for enabling SSTP is not listed in the
CLI. The command is listed only if you have configured a port-based VLAN.
To change a global STP parameter, enter a command such as the following at the global CONFIG
level.
BigIron RX(config) spanning-tree single priority 2
This command changes the STP priority for all ports to 2.
To change an STP parameter for a specific port, enter commands such as the following.
BigIron RX(config) spanning-tree single ethernet 1/1 priority 10
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