Enable ELRP on Extreme Switch to prevent Network loops

Problem Description : 

Network loop prevention causing a network outage. May see error message in switch logs similar to...

09/02/2014 11:51:14.92 &ltWarn:IPMC.Warning> Slot-1: Our own packet received. Mac address of the received packet is [2:4:96:34:8d:83],there could be physical loop in the network

09/02/2014 11:50:03.83 &ltWarn:IPMC.Warning> Slot-1: Previous message repeated 800 additional times in the last 71 second(s)

 Resolution : 

The Extreme Loop Recovery Protocol (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 a VLAN. When the packets transmitted by a switch are received back by that switch, this indicates a loop in the Layer 2 network.

After a loop is detected through ELRP, different actions can be taken such as blocking certain ports to prevent loop or logging a message to system log.

Telnet/SSH into switch and run these commands...

en elrp

configure elrp-client periodic "v244" ports all log-and-trap disable-port duration 300

configure elrp-client disable-ports exclude <Uplink port(s)>

sh elrp 

These commands enable elrp and activates it on the 244 VLAN on all ports. This configuration will disable the port if a loop is found for a 5 minute interval. It will continue to disable the port if it continues to find a loop back.

periodic means it sends a packet every 1 second.

It is suggested to exclude the uplink ports from being disabled so that ELRP does not disable these ports, causing the switch to lose connectivity. 

Update 9/5/2014 - Activated elrp on all residence hall switches. 

 Revision Date : 8/25/2015