You can tell if the loopback is set. Do a "show interface"
you can see where is says loopback set.
Serial0/0 is down, line protocol is down
Hardware is PQUICC with Fractional T1 CSU/DSU
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback set
Keepalive set (10 sec)
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Hope this helps.