ISDN Configuration

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May 26th, 2008
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We need to confgiure a backup route for our leased line to remote office.i have configured it using BRI.now in both the end it is showing line protocol is up(spoofing) but none of the data is travelling through this even after shuting down the serial interface


i have already configured static route in both end to reach the destination with higher AD than OSPF.


herewith i enclosed the output of Show int bri comand in both the routers


plz do let me know the issue if u can


Regards'

Bava



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Richard Burts Tue, 05/27/2008 - 02:53
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Bava


I agree with Krisztian that you have not yet given us enough information to be able to identify your problem. Please do provide configs.


You have not told us what mechanism you are using to direct traffic to the ISDN. I wonder if you are using backup-interface. Be aware that if you are configuring backup-interface then shutting down the primary serial interface will not cause ISDN to activate. You need to have the primary serial interface go protocol down (not admin down) for backup-interface to activate.


HTH


Rick

bava_ccna Wed, 05/28/2008 - 01:06
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hi Rick


I have used static route with higher AD for backup route.herewith i enclosed the configuration on both routers


can u do let me the real issue


Bava



Richard Burts Wed, 05/28/2008 - 03:45
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Bava


This is a start and does show us some things but not enough to be sure of what is the problem. Here is what I notice in what you have posted:

- in the show ip route you have shown only the connected routes. To understand the problem we need to see all the routes. And we need to see the configuration of the routes that you want to fail over to ISDN and the configuration of the routes with higher administrative distance that will cause the fail over.

- the ISDN interfaces are not doing authentication. I believe that they should be doing authentication.

- the dialer-group and dialer-list seem to be ok. whatever traffic is sent to the ISDN interface should be interesting and should bring up the interface and cause it to dial if it is not already active.


Please configure authentication on the ISDN interfaces and post the configuration of the routes.


HTH


Rick

Richard Burts Wed, 05/28/2008 - 07:28
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Krisztian


I wonder why you think that dialer string in the current configuration would not work?


HTH


Rick

Richard Burts Thu, 05/29/2008 - 03:14
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Krisztian


I would agree that many of us use dialer map more frequently and are more familiar with it. But either command should work ok - as far as specifying what number to dial to establish a connection.


HTH


Rick

bava_ccna Thu, 05/29/2008 - 22:44
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Yes....i got your point.Now i am getting Interface BRI 2/0 up,Line Protocol is up(Spoofing)..


Let me know what is the meaning of spoofing


Bava

Richard Burts Fri, 05/30/2008 - 03:38
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Bava


To understand spoofing as ISDN does it I think it is helpful to start with a fundamental principle of IOS: if an interface is not up IOS will remove that connected interface subnet from the routing table. IOS will not send any traffic to (or through) an interface that is not up since it has no entry in the routing table. But that is a potential problem with ISDN. When there is not an active connection the ISDN interface would be down and not have an entry in the routing table. But if the interface is down how would IOS send traffic to it which would cause the interface to place a call and become active (become up)? So the ISDN interface spoofs being up (it acts like it is up even when it is not really up). This allows IOS to put it into the routing table and to send traffic to the interface.


HTH


Rick

bava_ccna Fri, 05/30/2008 - 05:39
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Hi


So hear my connection is not UP...sine it is showing Line protocol up (Spoofing)...can i assume the problem might exist in the line


can any one help me


Bava

Richard Burts Fri, 05/30/2008 - 05:44
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Bava


It is possible that there is a problem in the line. But we do not have enough information available to us to know whether that is the case or not. Posting the output of show isdn status would help with this. (note that the connection not being up does not necessarily mean a problem in the line - not being up just means that there is no active call)


We have suggested a few changes and that you post the router configs. Seeing the configs in their current state would also be helpful.


HTH


Rick

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