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ISDN30 problem

I have two sites (A & B) connected using leased line as primary and ISDN30 as backup. The traffic flow is from Site-A to Site-B. ISDN30 provider use Alcatel ISDN switch in Site-A and Siemens ISDN switch in Site-B.

Following are setup in Site-A and Site-B routers.

- syslog (7)

- snmp-trap

- ip accounting of serial1/0:15 and dialer interface

- debug ppp authentication

- debug ppp negotiation

- debug isdn q921

- debug isdn q931

- debug dialer

- debug dialer packet

- leased line is monitored by WhatsUp

- leased line is monitored by MRTG

Configuration are okay and works according to the design that leased line is primary and ISDN30 is backup. Same configuration and rtouer model and connection setup is use in other sites without a problem.

According to ISDN provider, Site-B router ISDN30 is connecting to Site-A all 15 channels for 30 minutes and down for few seconds then connect again for 30 minutes all day long.

During the time ISDN30 provider sees the connection from the logs of their ISDN switch, I check the following;

- syslog >> no logs whatsoever about ISDN dialing or connecting

- snmp-trap messages >> no logs whatsoever about ISDN dialing or connecting

- show debug >> no logs whatsoever about ISDN dialing or connecting

- show ip accounting >> nothing

- show isdn active >> nothing

- show isdn history >> nothing

- MRTG >> doesn't show any break in leased line bandwidth utilization

- WhatsUp >> doesn't see leased line been down

- the routing table never change

- dialer interface is up/up (spoofing) >> normal

- serial1/0:15 is up/up (spoofing) >> normal

- serial1/0:0-14 and serial1/0:16-30 is down/down >> normal

- show isdn status

Global ISDN Switchtype = primary-net5

ISDN Serial1/0:15 interface

dsl 0, interface ISDN Switchtype = primary-net5

Layer 1 Status:


Layer 2 Status:

TEI = 0, Ces = 1, SAPI = 0, State = TEI_ASSIGNED

Layer 3 Status:

0 Active Layer 3 Call(s)

Active dsl 0 CCBs = 0

The Free Channel Mask: 0x00000000

Number of L2 Discards = 0, L2 Session ID = 10

Total Allocated ISDN CCBs = 0

Could it be a hardware or software problem of the router or ISDN switch in Site-B? Please advice the next step on identifying the root cause of the problem.


ROM: 12.4(13r)T

Cisco 2811 (revision 53.51) with 247808K/14336K bytes of memory.

2 FastEthernet interfaces

31 Serial interfaces

2 Serial(sync/async) interfaces

1 Channelized E1/PRI port

1 Virtual Private Network (VPN) Module

DRAM configuration is 64 bits wide with parity enabled.

239K bytes of non-volatile configuration memory.

250880K bytes of ATA CompactFlash (Read/Write)

Part of the ISDN config


isdn switch-type primary-net5


controller E1 1/0

pri-group timeslots 1-31


interface Serial1/0:15

no ip address

ip accounting output-packets

encapsulation ppp

dialer pool-member 1

dialer pool-member 2

isdn switch-type primary-net5

no cdp enable

ppp authentication chap

ppp multilink


interface Dialer2

ip address a.b.c.14

ip accounting output-packets

encapsulation ppp

dialer pool 2

dialer remote-name Site-A

dialer idle-timeout 30

dialer string 12345678

dialer load-threshold 1 either

dialer watch-disable 15

dialer watch-group 62

dialer-group 2

ntp disable

no cdp enable

ppp authentication chap

ppp multilink

ppp multilink fragment disable

ppp multilink links maximum 15

crypto map Site-A

Hall of Fame Super Silver

Re: ISDN30 problem

Hello Danilo,

if you connect only site A and site B the channel D interface should be associated to a single dialer

I see

dialer pool-member 1

dialer pool-member 2

I see you are using two dialers.

Your checks on router are deep and complete and you never see the router calling as claimed by the service provider.

It may be an hardware issue on service provider switch or on the ISDN PRI module on the router.

If you remove the two dialer pool-member to perform a test and then ask the service provider what they see.

If call activity stops there is something strange on your side otherwise it is on service provider side

Hope to help


Re: ISDN30 problem

Thanks Giuseppe.

I found what causing it to dial. However, since there is no traffic there (as they use the leased line) I can't find the reason why the 15 channel is up.

Hall of Fame Super Gold

Re: ISDN30 problem

Channel 15 it's the D channel and is supposed to be up all the time.

Re: ISDN30 problem

Hi Paolo,

Thank you for your reply. Yes you are right, the Serial1/0:15 and Dialer2 interface is up/up (spoofing) when it is enabled and the line is plugged, to masquerade it as up for it to include in the routing table.

What I don't understand is how come the telco detected 15 channels up when there is no data at all. Lets say that the ISDN dialed the remote site and gets authenticated/connected, but from what I understand, the B channel should be up only when there is data.

Hall of Fame Super Gold

Re: ISDN30 problem

How do you see that telco detected 15 channels up ?

Re: ISDN30 problem

Telco show me the log from their ISDN switch. But there is no log in my router (plus snmp-trap messages) about the 15 channels (even one of them) to be up.

Hall of Fame Super Gold

Re: ISDN30 problem

Reload router and start over. Keep a log or debug enable, you will be able to compare any discrepancy.

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