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ASK THE EXPERT-TROUBLESHOOTING DIAL ACCESS MODEM/ISDN ISSUES

Welcome to the Cisco Networking Professionals Ask the Expert conversation. This is an opportunity to get an update from Cisco expert Zulfiqar Ahmed on troubleshooting dial access modem/ISDN issues on Cisco access servers. Zulfiqar Ahmed, CCIE# 3960, is part of Technical Assistance Center (TAC) based out of San Jose, California where he currently holds the position of customer support engineer in Access-Cable team. He routinely provides escalation in complex access related issues, conducts trainings, and writes and reviews Cisco.com documents. His areas of expertise are troubleshooting & configuring Cisco access servers involving ISDN, Async, modems, DDR, AAA, PPP, etc.

Remember to use the rating system to let Zulfiqar know if you have received an adequate response.

Zulfiqar might not be able to answer each question due to the volume expected during this event. Our moderators will post many of the unanswered questions in other discussion forums shortly after the event. This event lasts through July 14, 2006. Visit this forum often to view responses to your questions and the questions of other community members.

19 REPLIES
Bronze

Re: ASK THE EXPERT-TROUBLESHOOTING DIAL ACCESS MODEM/ISDN ISSUES

Hi Ahmad,

I'm happy to start this interesting session.

I have a RAS that aggregates remote sites ISDN sites with one PRI E1. But i need to let ISDN users to access this RAS.

I read a document about configuring RAS for ISDN users, you need to create a rotary-group dialer interface for the ISDN users. My question is what is the rotary-group and also does this dialer interface for many ISDN users or you need to create dialer rotary group per each ISDN user?

Thanks in advance

Abd ALqader

Bronze

Re: ASK THE EXPERT-TROUBLESHOOTING DIAL ACCESS MODEM/ISDN ISSUES

Hi Abd Alqader,

Rotary group is basically when you want to bundle physical ISDN or async interfaces in a group for a thicker bandwidth pipe, for instance, in outbound

dialing :

interface BRI0

...

...

dialer rotary-group 5

...

interface BRI1

...

...

dialer rotary-group 5

...

interface BRI2

...

...

dialer rotary-group 5

...

interface dialer 5

...

...

This same config works for inbound callers also and it saves you from having to configure each and

every physical interface individually.

You can read more on dialer rotary concept in the following article:

Configuring MPPP for Multiple BRIs using Rotary Groups

http://www.cisco.com/en/US/partner/tech/tk713/tk507/technologies_configuration_example09186a00801035c1.shtml

As far as your question is concerned on whether you need to create a dialer rotary group for each ISDN user, as you might have guessed by now, that, no, you do not need that for rotary. All users will tie to the same rotary group. Instead, its the "dialer profiles" concept where you actually need a separate

dialer interface for each user or each remote site as you might want to negotiate different parameters with different remotes:

Configuring ISDN DDR with Dialer Profiles

http://www.cisco.com/en/US/customer/tech/tk801/tk133/technologies_configuration_example09186a0080093c2e.shtml

Now as far as your original requirement of "letting ISDN users access this RAS" is concerned, if you mean that you will have some ISDN users who will want to login to your RAS for admin/config or troubleshooting purposes, then you would actually need to configure this RAS for V.120 .

Following are some good docs on enabling V.120 :

Accepting V.120 and PPP Incoming Calls Using AAA

http://www.cisco.com/en/US/tech/tk801/tk133/technologies_configuration_example09186a0080093d2d.shtml

Access Server Dial-In IP/PPP Configuration With Dedicated V.120 PPP

http://www.cisco.com/en/US/tech/tk713/tk507/technologies_configuration_example09186a0080094551.shtml

Please let me know if you have any follow up questions or if I did not get your question right.

Thanks and Regards,

~Zulfiqar

Re: ASK THE EXPERT-TROUBLESHOOTING DIAL ACCESS MODEM/ISDN ISSUES

hi,

how many dialer profile can i create for one ISDN interface...? and can i run multiple dialer profile simultaneously?

and when ever we are going to configure the MLPPP then we can have multilink group and we add appropriate interface in to the multilink group and other way is virtual template... so can we distinguise both... which one is best...and which one is good?

regards

Devang

Bronze

Re: ASK THE EXPERT-TROUBLESHOOTING DIAL ACCESS MODEM/ISDN ISSUES

Hi Devang,

There is no limit on dialer profiles associated to the same physical interface. However, that may increase your size of the config and hence you are dependent on your NVRAM if you do not load your config from a TFTP server. If you do, then your RAM in the router will dictate how many dialers you can have in the config.

If you have a need for having a couple of hundreds of dialer profiles, you might want to look for 'Large Scale Dialout' (LSDO) feature as explained in this article :

Configuring and Troubleshooting Dialer Profiles

http://www.cisco.com/en/US/tech/tk801/tk133/technologies_tech_note09186a0080094e6c.shtml

And yes, you can run multiple dilaer profiles simultaneously and have MLPPP enabled as well on individual dialer interfaces.

Thanks and Regards,

~Zulfiqar

New Member

Re: ASK THE EXPERT-TROUBLESHOOTING DIAL ACCESS MODEM/ISDN ISSUES

Hi,

I have Cisco 3725 and ISDN PRI interface. I want to configure it, so first 20 MICA modems will be dedicated to first 20 timeslots and the other 10 to be dedicated to last 10 timeslots of the PRI interface. Cisco IOS 12.3(5b) is running on this access router.

Is this possible to configure on cisco 3725?

Bronze

Re: ASK THE EXPERT-TROUBLESHOOTING DIAL ACCESS MODEM/ISDN ISSUES

Hi Milevski,

Unfortunately, there is no one-to-one mapping between T1/E1 timeslots and internal modems that could be configured on Cisco routers. Hence this granularity is not possible.

Thanks and Regards,

~Zulfiqar

New Member

Re: ASK THE EXPERT-TROUBLESHOOTING DIAL ACCESS MODEM/ISDN ISSUES

Hi Zulfiqar,

We have an AS5300, ver. 12.2(2)XB12 and two T1's. How come the dial-up users connect at a different speed? For example, after they are connected, the Network Connections is minimized on the System Tray. If I do a right-click and select Status, under Speed, I see 31.2 kbps. If I disconnect and redial again, under Speed, I see 16 kbps. If I disconnect and redial again, under Speed, I see 44 kbps, etc. Is it normal that the users will connect at a different speed? She was the only one who uses the dial-up at the time. Please let me know if you have any questions or need additional information. Thanks.

Jill

Bronze

Re: ASK THE EXPERT-TROUBLESHOOTING DIAL ACCESS MODEM/ISDN ISSUES

Hi Jill,

Sounds like your calls from the same phone line is taking different circuit paths in the telco cloud which is totally expected. So depending on the line quality of those circuits, you will train at different speeds.

Thanks and Regards,

~Zulfiqar

New Member

Re: ASK THE EXPERT-TROUBLESHOOTING DIAL ACCESS MODEM/ISDN ISSUES

Hello, I am looking for the SNMP OID which give me information about active ISDN calls, maybe a table which includes the username or othet info.

I search alott of mibs but unable to find the OID

Maybe you can help. I want to querie, and trigger alaert when a specific ISDN call is actiev, filtered on username.

Regards

Bronze

Re: ASK THE EXPERT-TROUBLESHOOTING DIAL ACCESS MODEM/ISDN ISSUES

Hi Erwin,

You could probably poll .1.3.6.1.4.1.9.10.19.1.3.1.1.3 (List of users currently connected and authenticated) from CISCO-MODEM-MGMT-MIB as described in this article:

http://www.cisco.com/en/US/products/hw/univgate/ps501/products_implementation_design_guide_chapter09186a00800eaaff.html

Or try 1.3.6.1.4.1.9.9.163.1.2.3 from CISCO-CALL-TRACKER-MIB :

http://tools.cisco.com/Support/SNMP/do/BrowseOID.do?local=en&translate=Translate&objectInput=cctActiveTable

Thanks and Regards,

~Zulfiqar

New Member

Re: ASK THE EXPERT-TROUBLESHOOTING DIAL ACCESS MODEM/ISDN ISSUES

Hi Zulfiqar...

Q1.How does one handle the latency that occurs between the Primary(Serial 0) coming down and the secondary ISDN(Bri)taking over in DDR scenario? Can the internal Triggering Time be reduced or changed using any Cisco IOS instruction set or Command?

Q2.Can I use one Channel for Voice and one channel for Video On a Bri Port.If yes..could you reccommend any sample configuraton?

Q3.Is there any Cisco IOS command that can be used in a configuration that can shut down the ISDN port of the Router,the moment the incoming ISDN line voltage exceeds the normal level as a safety mechanism?

Q4.Do I need to do any additional configuration on a standard based third party Radius (AAA)Server,when a remote user tries to login into my Router that is preconfigured with "group radius" AAA capability?

Regards

Pradeep Varadarajan

D&E,I&M,CCNA,CCNP,CCIE-R&S(Written)

Bangalore

India.

Bronze

Re: ASK THE EXPERT-TROUBLESHOOTING DIAL ACCESS MODEM/ISDN ISSUES

Hi Pradeep,

(1) If you are using 'backup interface' command, then

you can make use of 'backup delay'. If you are using

dialer watch as your backup mechanism, you can use

'dialer watch-list x delay connect/disconnect y' as

discussed in the following doc :

Dialer Watch Connect Delay

http://www.cisco.com/en/US/partner/products/ps6350/products_configuration_guide_chapter09186a0080454ff6_4container_ccmigration_09186a0080440258.html

(2) Yes, that should be do-able, however I do not

have a sample config handy right now. You might want

to open up a case on this for further assistance.

(3) No, unfortunately thats not possible.

(4) As you mention, your router is already configured

with Radius/AAA so you won't have to change anything

if you are bringing in a new 3rd party Radius server.

You might probably want to go through these docs:

Configuring Authentication

http://www.cisco.com/en/US/products/ps6350/products_configuration_guide_chapter09186a00805010dd.html

Implementing the Server-Based AAA Subsystem

http://www.cisco.com/en/US/products/hw/univgate/ps501/products_case_study_chapter09186a00800ee066.html

Thanks and Regards,

~Zulfiqar

New Member

Re: ASK THE EXPERT-TROUBLESHOOTING DIAL ACCESS MODEM/ISDN ISSUES

Hi Ahmed

Could you guide me where to download this specific IOS that will support 1721 with 32D/16F & WIC-2AM.

12.2(4)YB was retired but couldn't find the alternative IOS based on migration path.

TIA

Bronze

Re: ASK THE EXPERT-TROUBLESHOOTING DIAL ACCESS MODEM/ISDN ISSUES

Hi Manuel,

IP feature set of any mainline 12.3 IOS will fit in 32D/16F that you have in this 1721 router, and should

support the WIC.

So, for instance, you could go to the latest 12.3 M, which is c1700-y-mz.123-19.bin without any problem.

Please note that 12.3T and 12.4/12.4T will require more memory. Hence, the maximum you could go to is 12.3(19) mainline with IP feature set.

Thanks and Regards,

~Zulfiqar

New Member

Re: ASK THE EXPERT-TROUBLESHOOTING DIAL ACCESS MODEM/ISDN ISSUES

Will the same 12.3 mainline support 1721 with 32D/16F & BRI w/dialer-watch feature?

Pls incl the url on your response.

Thanks again.

New Member

Re: ASK THE EXPERT-TROUBLESHOOTING DIAL ACCESS MODEM/ISDN ISSUES

Hello,

is it possible to use multiple multilink bundles between routers using a bundle with 2 E1's and a bundle wit 4 bri's without using "multilink bundle-name authenticated?

Regards Ben

Bronze

Re: ASK THE EXPERT-TROUBLESHOOTING DIAL ACCESS MODEM/ISDN ISSUES

Hi Ben,

I think with "multilink bundle-name authenticated" you are referring to this document :

Criteria for Naming Multilink PPP Bundles

http://www.cisco.com/en/US/tech/tk713/tk507/technologies_tech_note09186a0080093c49.shtml

However, please note that "multilink bundle-name authenticated" is already on by default.

Anyway, coming back to your main question, on whether or not you can bring up two separate MLP bundles, one comprising of 2 E1s, and one comprising of 4 BRIs, between the two routers, sure, you should be able to do that as long as you name them differently using "ppp chap hostname" command.

This is what I am talking about :

Multiple Multilink Bundles Between Routers

http://www.cisco.com/en/US/tech/tk713/tk507/technologies_configuration_example09186a0080093c1d.shtml

Thanks and Regards,

~Zulfiqar

New Member

Re: ASK THE EXPERT-TROUBLESHOOTING DIAL ACCESS MODEM/ISDN ISSUES

Hi Zulfiqar,

We have an AS5300 with one T1 PRI. When users dial in, we have their dial-in session configured for an interactive terminal. The users are prompted for username and password, but once that is entered, after about 60 seconds they get a 'password: timeout' and they are booted. We are authenticating users via RSA ACE RADIUS server, but we are seeing no authentication attempts in the logs. However, if a user puts in their user ID and passcode into the dial-up window before launching the call, the AS5300 will authenticate them so long as the token code does not change before the authentication takes place. How can we fix the AS5300 so that it works correctly with an interactive terminal session?

Thanks,

Coby Holloway

Bronze

Re: ASK THE EXPERT-TROUBLESHOOTING DIAL ACCESS MODEM/ISDN ISSUES

Hi Coby,

Your config and aaa debugs will be needed for further looking into this. However, based on past experience from relevant issues, I think it would be best if you open up a TAC case on this.

Thanks and Regards,

~Zulfiqar

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