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Rockwell Automation Publication 1783-UM007I-EN-P - December 2017 275
Configure Switch Features Chapter 3
BPDU Features
Switches exchange special frames that are called BPDUs to communicate
network information, to track changes, and to create the STP topology.
Because transmitted BPDUs reveal network information and received BPDUs
can influence your STP topology, consider enabling BPDU Filtering and
BPDU Guard on your access ports. These features help prevent a rogue device
from interfering with your STP topology. However, we recommend you use
these features with caution:
•
BPDU Filtering—This PortFast feature blocks all sending and receiving
of BPDUs through all ports. This feature effectively disables STP on
these ports and loops can result. If a BPDU is received, PortFast is
disabled on the port and the global STP settings apply.
•
BPDU Guard—This PortFast feature shuts down a port if it receives a
BPDU.
If you enable both of these features, BPDU Guard has no effect because BPDU
Filtering helps prevent the port from receiving any BPDUs.
Per Interface PortFast Table
Spanning tree requires an interface to progress through the listening and
learning states, to exchange information and establish a loop-free path before it
can forward frames. On ports that connect to devices such as workstations and
servers, you can allow an immediate connection. PortFast immediately
transitions the port into STP forwarding mode upon linkup.
To enable PortFast on an interface and apply the selected BPDU features to the
interface, select the interface, and then check Enable Port Fast.