Summit EXOS switches have a useful command to check for loops.

GNS3 setup above recreates a loop in VLAN DATA using ports 1 and 2 which are connected to a hub. Configure ELRP and generate test for a specific VLAN. Ports 1 and 2 are both members of VLAN DATA. No SPT protection (created VLAN and added ports to VLAN which is not bound to SPTD s0). Enable port 2 and test for loop.

#Configuring ELRP

enable elrp-client

conf elrp-client one-shot vlan DATA ports all interval 1 retry 5

EXOS-VM.5 # en port 2

* EXOS-VM.6 # conf elrp-client one-shot vlan DATA ports all interval 1 retry 5

Starting ELRP Poll

# LOOP DETECTED # — vlan “DATA” elrp statistics —

1 packets transmitted, 1 received, ingress port 2

. . .

Once finished disable it.

disable elrp-client

Note:

Make sure new VLANs are auto-bound with a Spanning Tree domain otherwise the ports may not be protected by SPT protocol and form loops.

enable stpd s0 auto-bind vlan DATA