There are two types of stack loopback tests: internal loopback test and external loopback test. The purpose of the internal loopback test is to verify that the stack ports are functional in each switch. The purpose of the external loopback test is to verify that the stack cables are functional.
For accurate results, the internal loopback test must be run before the external loopback test. The stack loopback tests can only be performed on a standalone unit with no traffic running on the unit.
To run the test, first use the #stack loopback-test internal command. To perform the external loopback test, connect the stack uplink port with the stack downlink port. Use the #stack loopback-test external command.
#stack loopback-test internal
#stack loopback-test external