ELRP messages spiking SNMP process

[Brian_Anderson]

Yesterday I was working at a customer site installing EMC. After getting the switches setup and into EMC with SNMPV3 several of the switches 'went down'. They were still accessible, so looked and SNMP process was high. Also noticed ALOT of ELRP loop messages coming into logs from the uplink ports. Opened a case with GTAC, narrowed down the issue with snmp (elrp was causing the spiked cpu) they tracked down the loop, and snmp process goes down on the affected switches. My question was why were these non-looped switches affected by the loop, the reason was 'because they are all connected to the core'. That just doesn't seem to make sense to me. Loop PROTECTION should be keeping other switches from being affected, however in this case that doesn't happen. On the switch where the loop was at, ELRP shut down the ports as configured, just would broadcast out 'LOOP' and send messages to other switches.

So the main question is, is spiking the snmp process on non-looped switches REALLY by design? If so, why? I couldn't get an satisfactory response yesterday, so posing the question here.

Thanks.

[Brian_Anderson]

not using policy.
# Module elrp configuration.
enable elrp-client
configure elrp-client periodic Default ports all interval 1 log-and-trap disable-port ingress duration 15
configure elrp-client periodic HS-Guest_Wifi ports all interval 1 log-and-trap disable-port ingress duration 15
configure elrp-client periodic HS-Mag ports all interval 1 log-and-trap disable-port ingress duration 15
configure elrp-client periodic HS-Staff_Wifi ports all interval 1 log-and-trap disable-port ingress duration 15
configure elrp-client periodic HS-Student_Wifi ports all interval 1 log-and-trap disable-port ingress duration 15
configure elrp-client periodic HS-Video ports all interval 1 log-and-trap disable-port ingress duration 15
configure elrp-client periodic HS-Voice ports all interval 1 log-and-trap disable-port ingress duration 15
configure elrp-client disable-port exclude 49
configure elrp-client disable-port exclude 50
configure elrp-client disable-port exclude 51
configure elrp-client disable-port exclude 52

[Jeremy_Gibbs]

What is the output of "show config elrp".

Do you have ELRP configured on all the edge switches as well? Also, are you using ExtremePolicy? What version of code are you running? In 16.x and some 21 and 22.x versions, ELRP does not work correctly with policy enabled.

[Patrick_Voss]

Hello Brian,

A loop affects the entire network. It sounds like all the switches were detecting the loop on the uplink but because that port is excluded from the disabled ports list it will only report it. If the log is generated on the switch then it will follow its configuration and send a trap to the server.

[Brian_Anderson]

Yes traps were enabled. Why do the traps get sent to other switches? Shouldn't it be sent to Netsight or something configured to receive the traps? In my opinion, for what it is worth, a loop getting prevented on a switch shouldn't affect other switches.