Switches - Juniper JUNOS OS 10.4 - FOR EX REV 1 Manual

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Understanding BPDU Protection for STP, RSTP, and MSTP on EX Series Switches
1756
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OS for EX Series Ethernet Switches, Release 10.4
setting the boundary for Bridge Protocol Data Units (BPDUs) sent by one MSTI. An MSTP
region is a group of switches that is defined by three parameters:
Region name—User-defined alphanumeric name for the region.
Revision level—User-defined value that identifies the region.
Mapping table—Numerical digest of VLAN-to-instance mappings.
An MSTP region can support up to 64 MSTIs, and each instance can support from 1 to
4094 VLANs. When you define a region, MSTP automatically creates an internal
spanning-tree instance (IST instance 0) that provides the root switch for the region and
includes all currently configured VLANs that are not specifically assigned to a user-defined
Multiple Spanning-Tree Instance (MSTI). An MSTI includes all static VLANs that you
specifically add to it. The switch places any dynamically created VLANs in the IST instance
by default, unless you explicitly map them to another MSTI. Once you assign a VLAN to
a user-defined MSTI, the switch removes the VLAN from the IST instance.
MSTP creates a Common and Internal Spanning Tree (CIST) to interconnect and manage
all MSTP regions and even individual devices that run RSTP or STP, which are recognized
as distinct spanning-tree regions by MSTP. The CIST views each MSTP region as a virtual
bridge, regardless of the actual number of devices participating in the MSTP region, and
enables MSTIs to link to other regions. The CIST is a single topology that connects all
switches (STP, RSTP, and MSTP devices) through an active topology, ensuring
connectivity between LANs and devices within a bridged network. This functionality
provided by MSTP enables you to better utilize network resources while remaining
backwards-compatible with older network devices.
Understanding STP for EX Series Switches on page 1751
Understanding RSTP for EX Series Switches on page 1753
Understanding VSTP for EX Series Switches on page 1760
Understanding Layer 2 Protocol Tunneling on EX Series Switches on page 1520
Example: Configuring Network Regions for VLANs with MSTP on EX Series Switches
on page 1775
Juniper Networks EX Series Ethernet Switches provide Layer 2 loop prevention through
Spanning Tree Protocol (STP), Rapid Spanning Tree Protocol (RSTP), VLAN Spanning
Tree Protocol (VSTP), and Multiple Spanning Tree Protocol (MSTP). BPDU protection
can help prevent STP misconfigurations that can lead to network outages.
A loop-free network is supported through the exchange of a special type of frame called
bridge protocol data unit (BPDU). Receipt of BPDUs on certain interfaces in an STP,
RSTP, VSTP, or MSTP topology, however, can lead to network outages. Enable BPDU
protection on those interfaces to prevent these outages.
Copyright © 2010, Juniper Networks, Inc.