Configuring Loopback Detection; In This Chapter - Alcatel-Lucent OmniSwitch 9900 Series Network Configuration Manual

7 Configuring Loopback
Loopback Detection (LBD) automatically detects the loop and shutdown the port involved in the loop.
This prevents forwarding loops on ports that have forwarded network traffic which has looped back to the
originating switch. LBD detects and prevents Layer 2 forwarding loops on a port either in the absence of
other loop detection mechanisms such as STP/RSTP/MSTP, or when these mechanisms cannot detect it
(for example, a client's equipment may drop BPDUs, or the STP protocol may be restricted to the network
edge).
A provider network with a set of multiple switches interconnected together can be logically viewed as a
large single switch. The large single switch provides service access points to customers' networks.
Configuration faults in customer networks can result in loops spanning both provider and customer
networks. This can result in broadcast storms. In order to protect provider's network from broadcast
storms, loops that involve SAP ports need to be detected and broken.
The LBD can detect and break loops created on the service-access interface.
For a service-access interface, LBD can be enabled for a specific port or linkagg. LBD for service-access
points allows shutting down only the specific interface of the link involved in the loop.
The switch can be configured to process LBD frames received from a different or remote system. The port
of the remote system is shut down, rather than passing it as invalid LBD frames.
When loopback occurs, a trap is sent and the event is logged. The port which is shutdown due to LBD is
automatically recovered if autorecovery-timer is set or the port can manually be enabled again when the
problem is resolved.

In This Chapter

This chapter describes the LBD feature and how to configure it through the Command Line Interface
(CLI). CLI commands are used in the configuration examples; for more details about the syntax of
commands, see the OmniSwitch AOS Release 8 CLI Reference Guide. This chapter provides an overview
of LBD and includes the following information:
•
"Quick Steps for Configuring LBD" on page 7-3
•
"LBD Overview" on page 7-4
•
"Configuring LBD" on page 7-7
•
"LBD for Service Access Interface" on page 7-8
•
"Verifying the LBD Configuration" on page 7-12
OmniSwitch AOS Release 8 Network Configuration Guide
Detection
December 2017 page 7-1