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New Member

804 and ISDN issue.

I have 2 locations that are doing this and I am at a loss as to why. Both locations have an ISDN for connectivity to our network. Both locations will get one of the 2 B channels up, but the second B channel never comes up. When I did a sh isdn hist shortly after rebooting the routers it shows that they are dialing the same phone number that is currently in use by the other channel. I do have two dialer strings with different numbers in the config, but the router will connect to one of the numbers and never attempt dial the second number.

I have verified that both spids are showing valid and I can manually trigger the router to dial the other number and get it to connect. The IOS version is 12.1.18.

Thanks in advance for any assistance.

New Member

Re: 804 and ISDN issue.


I had a similar issue, one spid would come up the other would not and everything looked fine. After about 3 days of battling my telco (Bell Canada) and getting some people that new what they where doing, they relized they had call forwarding on the isdn switch. This caused one end of the connection to forward the second spid to the first which busyed out and never made it to my router.

This may not apply to you since you can see a different number being dialed ????

Good luck!

Randy McIver


Cisco Employee

Re: 804 and ISDN issue.

You need to talk to telco to have them both the SPID's in hunt group at the receiving router side. So the second call on same SPID will be forwarded to the free spid.

Now you can configure the two dialer strings at calling side so that if first spid already have a active call then calling side will try the next number if it gets busy on the same first spid. Now that setup is not working in your case right?

Here is the perfact url for "Troubleshooting Second B-channel Call Failures on ISDN BRI Links"

New Member

Re: 804 and ISDN issue.

Thanks for the info. The url you sent had the fix. I added the following line to the bri sub interface config...

isdn fast-rollover-delay 5

and that caused it to use the second dialer string by telling the router not to use the first string for 5 second after a failure.

Thanks again for your help!