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No layer 3 with ISDN dial backup

I have set up a ISDN dial backup for a serial interface betwen two routers. When I issue a 'Shutdown' on the central router the remote router initiates the dial and connects but I cannot ping the remote router.

Using 'debug ppp auth' says that the CHAP authentication was successful. OSPF updates occur and go to the FULL state between the two.

Using 'sh ip ro' then shows that the routes are now all using the BRI1/0 interface on the first router & BRI0/0 on the second, but still no ping.

Using 'sh ISDN status' shows layer 3 status has one active call, load threshold is set to 128 (it does bring up both channel when set to 1).

The addresses for the interfaces are & both /30. 'sh int bri1/0' on the router recieving the call shows:

BRI1/0 is up, line protocol is up (spoofing)

Hardware is FECPM BRI

Description: *****Dial-backup*****

Internet address is

MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation PPP, loopback not set

Last input 00:00:05, output never, output hang never

Last clearing of "show interface" counters 1d04h

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: weighted fair

Why is the line protocol 'spoofing'? This is the thing that I believe is the problem but can't seem to find out why. The ISDN switch-type is set to basic-net3 for the UK.

Even after I've removed the backup commands from the serial interface, shutdown the serial port and removed the cable. configured the BRI as dial only gives the same results.

Any help appreciated.

Cisco Employee

Re: No layer 3 with ISDN dial backup

BRI interface is by default a DDR interface..It will remain as "spoofing" all the time, pretending to be up/up so the routing table can point to this interface,

even if you disconnect the bri cable..Pl. visit here for more

Here is the place which discuss that backup of serial interface with ISDN bri and running OSPF..

Just start with the basic..Without ospf, Just make sure that you can ping end to end first..