Loopback Through External CSU Back To Router Question

Unanswered Question
Apr 14th, 2007

Is it possible to successfully use a hard loop on the network side of a CSU and complete pings to yourself through the CSU and back(will the csu cause a problem in this)? I tried it once and it did not work when I think it should have. I am pretty sure this can be done however, and it could be a handy trick if so.

I have this problem too.
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pciaccio Sat, 04/14/2007 - 07:55

It is possible to run a loopback through the CSU. Make sure the timing on the network is set for internal liming. It is probably set for network or line timing. Set it for internal. That means that when you place a loopback on the network facing the CSU the CSU will time from itself. This clocking will clock the data off the DTE interface off the CSU. The router should come up to the loop OK, unless you have cabling problems... Good Luck....

stevennowell Sat, 04/14/2007 - 12:52

ahh...so that is probably why it failed in my case, because this csu would use timing from the network. One question though: in the case where I am working with a wic and an internal, I have successfully cleared errors many times with a loopback plug, but have never changed timing. Not sure how this factors in to this.

desai.jaideep Sat, 04/14/2007 - 08:55


(1)Make sure that the encap on serial is "hdlc"

(2) I dont know the make of your modem.But every modem have typically three types of loopbacks: Analog, Remote and Digital.

-Anaolog loopback will test a the conenctivity from the customer end modem to the router.

-Remote loopback when enabled, will test the connectivity between the pair on modems at your router.

-Digital will work the same as remote except the loop is provided at remote end.

Every lease line has two type of setup



Pls tell which setup is urs...

I any case, if you provide remote loop from modem1, the line protocol on router1 should be up and u should be able to ping ur serial interface.

Hope I have solved ur doubts. Pls comeback in case of more.




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