Different Kinds Of Bpdus; Protecting Switches From Incompatible Bpdus - Juniper EX9200 Features Manual

Spanning-Tree Protocols Feature Guide for EX9200 Switches

Different Kinds of BPDUs

Protecting Switches from Incompatible BPDUs

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Spanning-tree protocols such as Spanning Tree Protocol (STP), Rapid Spanning Tree
Protocol (RSTP), VLAN Spanning Tree Protocol (VSTP), and Multiple Spanning Tree
Protocol (MSTP) generate their own BPDUs. These peer STP applications use their
BPDUs to communicate, and ultimately, the exchange of BPDUs determines which
interfaces block traffic and which interfaces become root ports and forward traffic.
User bridge applications running on a PC can also generate BPDUs. If these BPDUs are
picked up by STP applications running on the switch, they can trigger STP miscalculations,
and those miscalculations can lead to network outages. Similarly, BPDUs generated by
STP protocols can cause problems if they are picked up by devices such as PCs that are
not using STP. Some mechanism for BPDU protection must be implemented in these
cases.
To protect the state of spanning-tree protocols on switches from outside BPDUs, enable
BPDU protection on the interfaces of a switch on which spanning-tree protocols are
configured and are connected to user devices (such as PCs)—for example, on edge ports
connected to PCs. Use the same strategy when a device on which STP is not configured
is connected to a switch through a trunk interface that forwards BPDUs generated by
spanning-tree protocols. In this case, you protect the device from BPDUs generated by
the STP on the switch.
To prevent a switch from forwarding BPDUs generated by spanning-tree protocols to a
device, you can enable
bpdu-block
On Juniper Networks EX Series Ethernet Switches that run Juniper Networks Junos
operating system (Junos OS) that supports the Enhanced Layer 2 Software (ELS)
configuration style, enable
level. To clear the BPDU error, use
On EX Series switches that run Junos OS that does not support the ELS configuration
style, enable
bpdu-block
clear the BPDU error, use clear bpdu-error
When an interface configured with BPDU protection encounters an incompatible BPDU,
it drops that BPDU and then, either shuts down or continues to receive packets other
than spanning-tree protocol BPDUs depending on the configuration defined in the
statement. If the interface continues to be open after dropping all incompatible
bpdu-block
BPDUs, all packets except incompatible BPDUs continue to ingress and egress through
the interface.
If the interface shuts down after dropping all BPDUs, you can re-enable the interface as
follows:
On Juniper Networks EX Series and QFX Series switches running Juniper Networks
Junos operating system (Junos OS) that supports the Enhanced Layer 2 Software
(ELS) configuration style:
on an interface.
at the
bpdu-block [edit protocols layer2-control ]
clear error bpdu interface
at the
[edit ethernet-switching-options
hierarchy
.
] hierarchy level. To
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