By you description of the problem, it sounds like you have HDLC configured on the router. It is probably transitioning every 30 seconds from up to down with a 10 seconds delay before going back to up. The reason why it is doing this is because it is not receiving keep alives from the remote end. Please verify that both ends are configured for HDLC. This is a propietary protocol to Cisco so if the other end is not a Cisco router then you will not be able to use HDLC which is the default encapsulation used by Cisco routers. You will need to use PPP instead. Now if both ends are Cisco routers and and both are configured for HDLC then you will have to figure out why you are not receiving keepalives from the remote end. This could be A possible CSU/DSU config issue or a Telco issue. I do not know whether or not you have a internal or external csu but, in either case their config has be checked and verified to make sure they match the provisioning of the circuit. If this is the case, then you will have to contact the telco to verify the circuit. You can also verify the circuit by using hard loopback plugs. This loopback plug can be placed on the remote side smartjack which should cause the near side router to go up/up(looped) if you have HDLC configured on the router. You can easily make a loopback plug by using one end of a rj45 cat5 cable and twisting 1 and 4 together then twist together 2 and 5 together. You can then insert this plug into the smartjack or the csu/dsu to verify your equipment and circuit.
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