Router S0/0 - up up "looped"

I'm working on a CCNA lab and trying to figure out why my S0/0 interface is showing - Serial0/0 is up, line protocol is up (looped).  Routers are Cisco 1700.  Version 12.2(4r)XL,

--Neither interface would allow me to put a clock rate. I am getting a message saying "
This command applies only to DCE interfaces".........However the book says (if you have a WIC-1DSU-T1, dont confuse with WIC-1T, use the service-module T1 clock source internal command instead. I did this and the other alternate command provided for the other interface.  Thats when both interfaces "went up up".......but looped
--On the hardware ports themselves it says - T1 DSU CSU
--I have green lights for CD next to port.
--LP is amber for 1 of the 2
--Tried other cables the lab provided.
--Tried shutting down the interfaces and bringing them back up.
--Cant ping
-- 2 IP addresses used for each Serial int - / 24 and /24.
- As of right now, no errors are showing up in the Interfaces but I did see some yesterday and cleared counters.
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Don JohnstonInstructorCommented:
What kind of serial interface do you have?

If you're seeing (looped), it could be that your cable is looping back to the interface.

Or if there's a CSU on the line, that could be in loopback mode.

Basically what's happening is the router is sending keepalives out the serial interface and they are coming right back in.

This might help.

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ctaddeoAuthor Commented:
Its fixed! As soon as I did "no loopback dte" on s0/0, it worked!  I can continue on with my lab now. Thank you for the help!!
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