Protocol both up and down at the 2 ends of a leased line?

Unanswered Question
Dec 10th, 2007

The HDLC T1 leased line that we use to connect to a partner's site, has always been working fine. Recently, in several occasions, some Telco's problems brought the protocol down on our serial interface, but the remote partner's serial interface didn't notice the event and kept the prococol up. Remote HSRP did not activate the standby router and the 2 sites became disconnected. I know this can appen with frame-relay and DSL connections, but I didn't expect from point-to-point Leased lines. Shutting down administratively our serial interface finally brings down the remote line protocol. Telco's support says that everything is OK on their side and debugging HDLC at both ends during normal operations shows two consistent sequences of packets; the keepalives are of course set. Should I change the remote serial interface?

I have this problem too.
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ccbootcamp Mon, 12/10/2007 - 08:32

Did Telco through a loop in the line somewhere? If so, that could keep the interface up/up on one side

I've seen all sorts of weird things happen with bad smartjacks (NIUs). However, if telco can loop your CSU/DSU, then odds are, the smartjack is okay. Make sure neither of your CSU/DSUs are in a looped state. If you have confirmed that neither CSU/DSU is in a looped state, and Telco can loop both CSU/DSUs, then yes, time to replace something. I am assuming that you have a WIC-1DSU-T1 (or equiv.) type WIC in your routers. Replace the one that is up/up first and see if that solves your problem.


(please rate the post if this helps!)

sisal Tue, 12/11/2007 - 07:35

Thank you for your reply. YES: I confirm that neither CSU/DSU is in a looped state, and Telco can loop both CSU/DSUs. However CSU/DSUs are external boxes owned and managed by TELCO and connected to the routers via Serial Interfaces (our is a WIC-1T: old Cisco 1 Port Serial WAN Interface Card with DB60 connector, but don't know our partner's type). So I imagine I hawe to change the remote serial WIC. However under normal conditions it works perfectly!! Do you think it's worth trying the substitution without further investigation? (keep in mind that I cannot decide independently but have do agree the substitution with my partner).

P.S. I'm not familiar with American terms. Even if I imagine that "smartjack" refers to the end of TELCO's wiring where the CSU/DSU connects, is there another "name" for it apart from NIU or NID?. Here in Europe the DEMARC is the CSU/DSU and I find sometimes difficult to talk with Telco's support.

Thanks again, Piero.


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