Brocade Mobility RFS7000-GR Controller System Reference Guide (Supporting software release 4.1.0.0-040GR and later) - Manual (Page 233)

Brocade Mobility RFS7000-GR Controller System Reference Guide 219
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Multiple spanning tree
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6. Modify the AP Image File as necessary. You can browse the switch filesystems using the
browser icon. AP images must be on the flash, system, nvram or usb filesystems in order for
them to be selected.
7. Click the OK button to save the changes and return to the AP Firmware tab.Multiple Spanning
Tree
Multiple spanning tree
Multiple Spanning Tree Protocol (MSTP) provides a VLAN-aware protocol and algorithm to create
and maintain a loop-free network. It allows the configuration of multiple spanning tree instances.
This ensures a loop-free topology for 1 or more VLANs. It allows the network administrator to
provide a different path for each group of VLANs to better utilize redundancy.
MSTP allows rapid convergence similar to Rapid Spanning Tree Protocol (RSTP). RSPT is an
independent protocol and MSTP does not use RSTP. Since MSTP allows VLANs to be grouped in an
instance, each instance can have its own spanning-tree topology independent of other
spanning-tree instances. This architecture provides multiple forwarding links for data traffic, load
balancing and therefore, reduces the number of spanning-tree instances required to support a
large number of VLANs.
Using MSTP, the network can be divided into regions. All switches within a region use the same
VLAN to instance mapping. The entire network runs a spanning tree instance called the Common
Spanning Tree instance (CST) that interconnects regions as well as legacy (STP and RSTP) bridges.
The regions run on a local instance for each configured MSTP instance.
The network-wide spanning tree for instance 0 is known as the Common Spanning Tree (CST). A
spanning tree for any other instance, which is local to a region, is known as an Internal Spanning
Tree (IST). The Common and Internal Spanning Tree (CIST) (which consists of the CST as well as all
ISTs across regions) interconnects all bridges in the network.
The following definitions describe the STP instances that define an MSTP configuration:
• Common Spanning Tree (CST) – MSTP runs a single spanning tree instance (called the
Common Spanning Tree) that interconnects all the bridges in a network. This instance treats
each region as a single bridge. In all other ways, it operates exactly like Rapid Spanning Tree
(RSTP).
• Common and Internal Spanning Trees (CIST) – CIST contains all of the ISTs and bridges not
formally configured into a region. This instance interoperates with bridges running legacy STP
and RSTP implementations.
• Multiple Spanning Tree Instance (MSTI) – The MSTI is identified by an MSTP identifier
(MSTPid) value from 1 to 15. This defines an individual instance of a spanning tree. One or
more VLANs can be assigned to an MSTI. A VLAN cannot be assigned to multiple MSTIs. The
multiple spanning tree instance 0 is always present. VLANs not explicitly assigned to an
instance are assigned to instance 0.
• MSTP Region – These are clusters of bridges that run multiple instances of the MSTP protocol.
Multiple bridges detect they are in the same region by exchanging their configuration digest
(which is dependent on the VLAN to instance mapping), region name and revision-level. If you
need to have two bridges in the same region, the two bridges must have identical VLAN to
instance mappings, region names and revision-levels.