Using Standalone Elrp To Perform Loop Tests; About Standalone Elrp - Extreme Networks ExtremeWare XOS Guide Manual

Troubleshooting

Using Standalone ELRP to Perform Loop Tests

Having a tool to determine if the network has any loops is extremely useful. There are various other
protocols that can exploit this tool to prevent network loops. There are also situations where you might
want to check the topology for the existence or absence of a loop.
ExtremeWare XOS 11.1 introduces support for the Extreme Loop Recovery Protocol (ELRP). ELRP
allows you to prevent, detect, and recover from Layer 2 loops in the network. You can use ELRP with
other protocols such as ESRP, as described in the section
protocols such as Ethernet Automatic Protection Switching (EAPS) requires that a network have a ring
topology to operate. In this case you can use ELRP to ensure that the network has a ring topology.
ELRP is used to detect network loops in a Layer 2 network. A switch running ELRP transmits multicast
packets with a special MAC destination address out of some or all of the ports belonging to a VLAN.
All of the other switches in the network treat this packet as a regular, multicast packet and flood it to all
of the ports belonging to the VLAN. If the packets transmitted by a switch are received back by that
switch, this indicates a loop in the Layer 2 network.
Once a loop is detected through ELRP, different recovery actions can be taken such as blocking certain
ports to prevent loop or logging a message to system log. The action taken is largely dependent on the
protocol using ELRP to detect loops in the network.
Using ELRP with ESRP is one way you can use ELRP. For more information about configuring ESRP
and ELRP, see the section
"standalone" ELRP commands to determine whether a network has an Layer 2 loop or not. The
remaining sections describe how to configure standalone ELRP on your switch.

About Standalone ELRP

Standalone ELRP gives you the ability to send ELRP packets, either periodically or on an ad hoc "one-
shot" basis on a specified subset of VLAN ports. If any of these transmitted packets is received back
then standalone ELRP can perform a configured action such as sending a log message to the system log
file or sending a trap to the SNMP manager.
Standalone ELRP allows you to:
Configure ELRP packet transmission on specified VLANs.
●
Specify some or all the ports of VLAN for packet transmission.
●
NOTE
Reception of packets is not limited to any specific ports of the VLAN and cannot be configured.
Configure transmission of ELRP packets on specified ports of a VLAN periodically with the added
●
ability to configure the interval between consecutive timings.
Save and restore standalone ELRP configuration across reboots.
●
ExtremeWare XOS 11.1 Concepts Guide
"Using ELRP with ESRP" on page
"Using ELRP with ESRP" on page
345. Another way to use ELRP is to invoke
345. Other
440