ISDN BRI Backup interface problem

Unanswered Question
Oct 22nd, 2008

Hi ALL

I had recently a strange problem in ISDN.

A C2600 router, that has a microwave link as primary and ISDN as Backup interface, is working very fine.

When upgrading the same configuration to new router C2811, the BRI interface is always UP, when i debugged the dialer, i found that traffic is being sent from the BRI interface sourve to 224.0.0.10(eigrp multicast),

Jul 25 23:06:35 : BR0/0/0 DDR: place call

Jul 25 23:06:35 : BR0/0/0 DDR: Dialing cause ip (s=172.17.1.18, d=224.0.0.10)

Jul 25 23:06:35 : BR0/0/0 DDR: Attempting to dial 01966115

Jul 25 23:06:36 : %LINK-3-UPDOWN: Interface BRI0/0/0:2, changed state to up

Jul 25 23:06:36 : %ISDN-6-CONNECT: Interface BRI0/0/0:2 is now connected to 019

So how could applying exactly the same config on 2 different routers, create such a difference???

(config attached)

Please advise

Attachment: 
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shillyar Wed, 10/22/2008 - 10:41

Hello,

your access/dialer list is wrong this should have never worked right prior as you have dialer-list 1 ip permit in that case it would always dial all the time

you need to add

dialer-list 1 list 101

access-list 101 deny ip any host

acesss-list 101 deny eigrp any any

access-list 101 permit x.x.x.x x.x.x.x( interesting traffic that you want to trigger the dial)

Thx Steve

jorjes1984 Wed, 10/22/2008 - 11:21

hello

i agree with you totally

i even personally dont do such type of configuration, i always configure the ISDN as default gateway with a higher AD

but my task was just to change the Router's type, and i noticed that thing.

But the weird thing is that on the older router, 2610 (IOS: c2600-ik9o3s3-mz.123-6e.bin) was not showing that problem, i tried to shut/unshut the interface multiple tims, and it worked fine.

could there be any commands enabled by default on the C2811 (new router) that were not enabled by default on the older one that my be causing the problem??

shillyar Wed, 10/22/2008 - 11:33

Id have to say no as the def for the dialer list is not haveing a dialer list so it would never dial. The conf is just incorrect. Id have to say it been going on for a long time and just no one noticed it as with "ip permit" that line will always be flapping and dialing 24x7

Thx Steve

jorjes1984 Wed, 10/22/2008 - 11:43

I will try the suggested config in the next intervention.

Just i want to clear something,

in the access list u suggested, what do u mean by the first line

"access-list 101 deny ip any host"

deny ip any to which host?

Regds

shillyar Wed, 10/22/2008 - 12:11

That should block normal broadcast from triggering the dial. It's just by habit I always used it back in the day when I did DDR every day.

Thx Steve

jorjes1984 Fri, 10/24/2008 - 10:45

hey there

the

deny eigrp any any

permit ip any any

solved the problem as expected.

But while troubleshooting i found something that i would like to ask about:

in the older router (C2610), when i put "BACKUP INTERFACE BRI0/0/0" under the serial interface,

the BRI interface shows as STANDBY/shutdown in the SHOW IP INT BRIEF output, so even if there was a Permit ip any any in the dialer list, there is nothing that could initiate a call as the interface is shut.

Router(C2620)#show ip int brief

Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 192.0.8.1 YES NVRAM up up

FastEthernet0/1 unassigned YES NVRAM administratively down down

BRI0/0/0 172.17.1.18 YES NVRAM standby mode/disabled down

BRI0/0/0:1 unassigned YES unset administratively down down

BRI0/0/0:2 unassigned YES unset administratively down down

while in the C2811 router, the same config was applied, but in the SHOW IP INT BRIEF output, the BRI interface is showing as UP UP, and sub channel are down,but all the IP traffic is passing though the primary interface, but in this case the eirgp traffic initiated from the interface BRI is able to initiate the call

Router(c2811)#show ip int brief

Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 192.0.4.1 YES NVRAM administratively down down

FastEthernet0/1 unassigned YES NVRAM administratively down down

BRI0/0/0 172.17.1.26 YES NVRAM up up

BRI0/0/0:1 unassigned YES unset down down

BRI0/0/0:2 unassigned YES unset down down

does anyone knows why in the old Router/IOS version, the BACKUP INTERFACE operate differently(shuts the BRI interface when in standbye) from when being applied on a newer IOS/ROUTER (BRI is physically UP, not passing IP traffic, but passing eigrp traffic)?

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