Router A can call Router B, Router B can't call Router A

Unanswered Question
Sep 9th, 2007

Hi,


I have a Cisco3640 and a Cisco2503 connected via an ISDN simulator. The 2503 can call the 3640 with no problems, and once connnected they can ping back and forth with no problems.


However, if the 3640 tries to establish a connection with the 2503, either by manually calling (isdn call int bri2/0 21) or by sending some interesting traffic, the call doesn't come up. I have swapped the cables on the ISDN simulator and changed the numbers being dialed - the 3640 still couldn't call the 2503 - so it is not as if the simulator is configured to only call one-way.


If anyone has any suggestions, that would be great - thanks!


Here is the configuration and version of the two routers:


Configuration of Cisco3640:


interface BRI2/0

ip address 10.0.0.1 255.255.255.0

encapsulation ppp

dialer string 21

dialer-group 1

isdn switch-type basic-net3

end


dialer-list 1 protocol ip permit


Version:


Cisco Internetwork Operating System Software

IOS (tm) 3600 Software (C3640-IK9O3SW6-M), Version 12.2(8)T, RELEASE 2


Configuration of Cisco2503:


interface BRI0

ip address 10.0.0.2 255.255.255.0

no ip directed-broadcast

encapsulation ppp

dialer string 11

dialer-group 1

isdn switch-type basic-net3

end


dialer-list 1 protocol ip permit


Version:


Cisco Internetwork Operating System Software

IOS (tm) 2500 Software (C2500-D-L), Version 12.0(5)T, RELEASE SOFTWARE (fc1)


Attached are the following files:


3640-fail-debug_and_status.txt - this is the debug and ISDN status output from the 3640, when the 3640 tries to connect to the 2503 and fails.


2503-fail-debug.txt - this is the debug from the 2503, when the 3640 tries to connect to it.


2503-3640-OK-debug_and_status.txt - this is the debug from both routers from a successful attempt (when the 2503 calls the 3640).



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lgijssel Sun, 09/09/2007 - 10:23

Might be a ppp authentication issue.

Check that authencation can work two ways.

Otherwise: Can you post the output from "deb ppp neg" and "deb ppp authen"?


regards,

Leo

Richard Burts Sun, 09/09/2007 - 14:29

James


I would agree with Leo that seeing debug ppp nego and debut ppp authen might be helpful. I would also like to see the output of debug isdn q931.


HTH


Rick

james.leavers Mon, 09/24/2007 - 11:24

Sorry about the delay!


I actually removed ppp authentication for testing purposes as per the config, so would there be anything to be seen is debug pp auth was used?


debug isdn q931 was on at the time though, it should have been in the attachment.

Richard Burts Mon, 09/24/2007 - 12:25

James


From the log on the 2503 there is a call proceeding which is an indication that the call is connecting at 1:35:33:

01:35:33: ISDN BR0: TX -> CALL_PROC pd = 8 callref = 0xE0

and there is a corresponding debug record on the 3640. The debug on the 2503 then shows the call as connected.


Then at 1:35:57 the 2503 disconnects the call:

01:35:57: BRI0:1 DDR: disconnecting call


So there is an interval of about 24 seconds in which something is happening. I would suggest that debug ppp negotiation would be a good next step in figuring out what is going on.


HTH


Rick

james.leavers Sun, 10/07/2007 - 08:16

Hi,


Thanks for the reply - I have attached two files:


"Success - debug ppp neg.txt" - this is the output from debug ppp neg for a successful call, i.e. one from the 2503 to the 3640.


"Fail - debug ppp neg.txt" - this is the output from the failed call, i.e. 3640 to 2503.


There is no output from the 3640 during a failed attempt.


There is output from the 2503 during a failed attempt. It has "Phase is ESTABLISHING, Passive Open" whereas when it places the call it starts with "Phase is ESTABLISHING, Active Open".



Richard Burts Sun, 10/07/2007 - 12:39

James


Thanks for posting the additional debug information. The debug of the failing attempt pretty clearly shows that the 2503 is attempting to negotiate but the 3640 is not negotiating. I am a bit puzzled why the 3640 will negotiate when it is called but does not negotiate when it is calling. Can you post the entire config of the 3640? I wonder if there is something that we have not seen yet that might help to explain this.


HTH


Rick

james.leavers Sat, 01/12/2008 - 05:43

Hi,


I have finally found time to revisit this! The 3640 is my main lab router so it normally has a lot of functions when compared to the 'lesser' routers, so I thought there was a possibility that something else in the configuration was interfering.


So I have stripped everything out apart from the ISDN configuration on both routers, but the situation is still the same.


I have attached the configuration of both routers.



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