User Manual

Configure Switching Information
270
M4200 and M4300 Series ProSAFE Managed Switches Web Management User Manual
If the source MAC address matches the MAC address of the switch, the switch can perform
one of the following actions, depending on how you configure the action:
• The port is shut down.
• A log message is generated. (If a syslog server is configured, the log message can be
sent to the syslog server.)
• The port is shut down and a log message is generated.
If loop protection is disabled, the multicast packet is silently dropped.
Loop protection is not intended for ports that serve as uplinks between spanning tree–aware
switches. Loop protection is designed for unmanaged switches that drop spanning tree
bridge protocol data units (BPDUs).
You need to enable the feature globally before you can enable it at the port level so that the
system policy filter can be installed.
Loop Protection and PDU Packet Transmission
Loop protection sends loop protocol packets from all ports on which it is enabled. You can
configure the interval (1 to 5 seconds) between two successive loop protection PDU packets.
The default interval is 5 seconds. If the switch receives a loop protocol packet on a port for
which the action is set to shut down the port, the port can no longer receive and send frames.
Loop protection operates at a port level, regardless of VLAN assignment and membership,
detecting loops across VLANs.
Loop Protection and Spanning Tree Protocol
Loop protection does not impact end nodes and is not intended for ports that serve as uplinks
between spanning tree–aware switches. Loop protection can coexist with Spanning Tree
Protocol (STP). You can enable both loop protection and STP on a port because these
features function independently of each other. STP does not bring a port down when a loop is
detected but keeps the port in blocking state. Because PDUs are allowed in a blocking state,
loop protection packets are received and loop protection brings down the port that is involved
in the loop (if the configured action is to shut down the port).
Configure the Global Loop Protection Settings
Before you can configure loop protection for individual ports (see Configure the Loop
Protection Settings for Ports and View the Loop Protection State on page 272), you must
globally enable and configure loop protection.
 To globally enable and configure loop protection:
1. Launch a web browser.
2. Enter http://<ipaddress> in the web browser address field.
The login window opens.