/Net/cernvax/userd/tbl/denise/CircuitDown.html

# DECnet Circuits down

If the ALARM system indicates that a DECnet circuit is down then normally the traffic will flow over a backup route. There is usually a degradation in performance but DECnet connections will continue to work. The only circuit without a backup route is x25-spain. (The backup route to Desy, via INFN, can be unstable). You can check the status of DECnet circuits on a router, e.g. cernr1, using the following NCP command from any DECnet node:

    			NCP> tell cernr1 show know circuits

The normal status of a DECnet circuit is 'on' followed by the DECnet node number of the adjacent router. A DECnet circuit is considered down when its status is 'on -synchronizing'. This means that the circuit is continually trying to restart itself but without success. When a DECnet circuit is down, this usually indicates a problem with the leased line to the remote site. If the circuit name starts with the prefix 'X25-' then the circuit requires X.25 to be functioning correctly. If an individual DECnet circuit is down, the problem is generally resolved after intervention of the PTT, although you should first try to contact the remote DECnet manager (see section 'HEP DECnet Contacts') to ensure that the problem is not due to changes at the remote site. If several DECnet circuits with the prefix 'X25-' are down simultaneously, this tends to indicate an X.25 problem at CERN.

If several X25-xxx circuits are down on the same router, it may be necessary to restart CAMTEC line 1 on the appropriate CAMTEC switch. CERNR1 is connected to CAMTEC switch 0 and CERNR2 is connected to CAMTEC switch 1.

There is a known problem with the line between the CAMTEC switch and the DECnet routers. When a router reboots (for whatever reason) the CAMTEC line generally needs to be restarted. To check for this situation on cernr1, invoke NCP on any DECnet node and type:

    			NCP>tell cernr1 sho know dte

If the dte is in state 'unsynchronized' then the X.25 line must be reset from the CAMTEC side. Resetting the line from the DECnet router has no effect.

See also the normal status of circuits on cernr1 and cernr2.