Juniper EX9200 Features Manual page 241

Overview and Topology
Copyright © 2017, Juniper Networks, Inc.
NOTE: By default, RSTP is enabled on all EX Series switches.
EX Series switches provide Layer 2 loop prevention through Rapid Spanning Tree protocol
(RSTP) and Multiple Spanning Tree Protocol (MSTP). All spanning-tree protocols use
a special type of frame called a BPDU to communicate. Other devices also use BPDUs—PC
bridging applications, for example, generate their own BPDUs. These different BPDUs
are not compatible. When BPDUs generated by spanning-tree protocols are transmitted
to a device that uses another type of BPDU, they can cause problems on the device.
Similarly, if switches within a spanning-tree topology receive BPDUs from other devices,
network outages can occur because of the miscalculations caused by the outside BPDUs.
Therefore, you must configure BPDU protection on interfaces in a spanning-tree topology
to avoid network outages.
This example explains how to block outside BPDUs from reaching a switch interface
connected to devices that are not part of the STP topology. In this scenario, an interface
is shutdown when it encounters an outside BPDU.
Figure 3 on page 220 shows the topology for this example. Switch 1 and Switch 2 are
connected through a trunk interface. Switch 1 is configured for RSTP and Switch 2 does
not have a spanning-tree protocol configured on it.
This example configures downstream BPDU protection on Switch 2 interfaces
and . When BPDU protection is enabled, the switch interfaces will shut down
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if BPDUs generated by the laptops attempt to access Switch 2.
CAUTION: When configuring BPDU protection on an interface without
spanning trees connected to a switch with spanning trees, be careful that
you do not configure BPDU protection on
BPDUs being received on switch interfaces (such as a trunk interface) that
you intended to have receive BPDUs from a switch with spanning trees.
Chapter 10: Using BPDU Protection, Root Protection, and Loop Protection
all
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interfaces. Doing so could prevent
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