Brocade Converged Enhanced Ethernet Administrator's Guide v6.1.2_cee (53-1001258-01, June 2009)

Converged Enhanced Ethernet Administrator’s Guide 39
53-1001258-01
Chapter
4Configuring STP, RSTP, and MSTP using the CEE CLI
In this chapter
•STP overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
•RSTP overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
•MSTP overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
•STP, RSTP, and MSTP configuration guidelines and restrictions . . . . . . . . . 44
•Default STP, RSTP, and MSTP configuration . . . . . . . . . . . . . . . . . . . . . . . . . 44
•STP, RSTP, and MSTP configuration procedures . . . . . . . . . . . . . . . . . . . . . . 45
STP overview
The IEEE 802.1D Spanning Tree Protocol (STP) runs on bridges and switches that are
802.1D-compliant. STP prevents loops in the network by providing redundant links. If a primary link
fails, the backup link is activated and network traffic is not affected. Without STP running on the
switch or bridge, a link failure can result in a loop.
When the spanning tree algorithm is run, the network switches transform the real network topology
into a spanning tree topology in which any LAN in the network can be reached from any other LAN
through a unique path. The network switches recalculate a new spanning tree topology whenever
there is a change to the network topology.
With STP, data traffic is allowed only on those ports that are part of the spanning tree topology.
Ports that are not part of the spanning tree topology are put in a blocking (inactive) state. They are
kept in the blocking state until there is a break in the spanning tree topology, at which time they
are activated to provide a new path.
The STP interface states for every Layer 2 interface running STP are as follows:
• Blocking—The interface does not forward frames.
• Listening—The first transitional state after the blocking state when the spanning tree
determines that the interface should participate in frame forwarding.
• Learning—The interface prepares to participate in frame forwarding.
• Forwarding—The interface forwards frames.
• Disabled—The interface is not participating in spanning tree because of a shutdown port, no
link on the port, or no spanning-tree instance running on the port.