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Cisco Certification Introduction To ISDN Part VThe major reason I recommend getting your hands on real Cisco equipment rather than a simulator is that real Cisco routers give you the chance to practice and learn show and debug commands. Cisco Certification Introduction To ISDN Part I Cisco Certification: Introduction To ISDN, Part I From the CCNA to the CCIE, ISDN is one of the most important technolgies youll work with. Its also very common in the field; ISDN is frequently use.. Activated dsl 0 CCBs = 0 The Free Channel Mask: 0x80000003 Once in a while, you'll get this output from show isdn status: R2#show isdn status The current ISDN Switchtype = basic-ni1 ISDN BRI0 interface Layer 1 Status: ACTIVE Layer 2 Status: Layer 2 NOT Activated Spid Status: TEI Not Assigned, ces = 1, state = 3(await establishment) spid1 configured, no LDN, spid1 NOT sent, spid1 NOT valid TEI Not Assigned, ces = 2, state = 1(terminal down) spid2 configured, no LDN, spid2 NOT sent, spid2 NOT valid Check your running configuration, and if the SPIDs look good, simply close the BRI interface and open it again. Then run show ISDN status again. If you then see 'spids are valid”, you're ready to proceed. If you still see a message that the spids are invalid, you've most likely mistyped the SPID. Show Access-List What's this command got to do with ISDN? Everything. Remember how the ISDN link comes up in the first place? Interesting traffic. By default, there is no interesting traffic. You define interesting traffic with the dialer-list and dialer-group commands, AND the access-list command. If you have a problem with your link never coming up or with it coming up and staying up, use this command to see what traffic has been defined as interesting. Show Dialer Another helpful command to determine why an ISDN link is coming up and staying up. This command shows you how many successful calls and failed calls have taken place, what the current idle-timer value is (by default, it's 120 seconds), and most importantly, what the source and destination was for the current interesting traffic: R1#show dialer BRI0 - dialer type = ISDN Dial String Successes Failures Last called Last status 8358662 1 0 00:00:59 successful The Brief History of Cisco Certifications The Brief History of Cisco Certifications Even young people can remember the old days when network administrators were more often associated for being the person sitting next to a computer system rat.. 0 incoming call(s) have been screened. 0 incoming call(s) rejected for callback. BRI0:1 - dialer type = ISDN Idle timer (120 secs), Fast idle timer (20 secs) Wait for carrier (30 secs), Re-enable (15 secs) Dialer state is data link layer up Dial reason: ip (s=172.12.21.1, d=172.12.21.2) Time until disconnect 62 secs Connected to 8358662 (R2) Here, you can see that the idle-timer value is at its default, that there are 62 seconds left until the link comes down (unless interesting traffic resets the timer), and that the source of the interesting traffic was 172.12.21.1 and the destination is 172.12.21.2. If that destination is the multicast address of a routing protocol - say, 224.0.0.5 for OSPF - you know what traffic is keeping the line up. Show ISDN History Want to see what calls have been made in the last 15 minutes? Just run this command. It's helpful if you're walking in to an ISDN troubleshooting situation and want to see what calls have been made. R1#show isdn history-------------------------------------------------------------------------------- ISDN CALL HISTORY--------------------------------------------------------------------------------History table has a maximum of 100 entries.History table data is retained for a maximum of 15 Minutes.--------------------------------------------------------------------------------Call Calling Called Remote Seconds Seconds Seconds ChargesType Number .Number Name Used Left Idle Units/Currency-----------------------------------------------------------------------------------------------------------Out 8358662 R2 121 0Out 8358662 R2 121 0----------------------------------------------------------------------------------------------------- Debug PPP Negotiation Not only do you need to know this command for your CCNA and CCNP exams, you MUST know it to be an effective ISDN troubleshooter. When PPP authentication is first configured, it's simple to mistype a password, or forget to configure a 'username / password” combination. Instead of continually reading your running configuration to see what the problem is, run debug ppp negotiation and send a ping to bring the line up. You'll quickly see where the problem is. R2#debug ppp negotiation PPP protocol negotiation debugging is on R2#ping 172.12.21.1 BR0:1 PPP: Phase is AUTHENTICATING, by both BR0:1 CHAP: O CHALLENGE id 1 len 23 from "R2" BR0:1 CHAP: I CHALLENGE id 1 len 23 from "R1" BR0:1 CHAP: O RESPONSE id 1 len 23 from "R2" BR0:1 CHAP: I SUCCESS id 1 len 4 BR0:1 CHAP: I RESPONSE id 1 len 23 from "R1" BR0:1 CHAP: O SUCCESS id 1 len 4 By mastering these simple ISDN show and debug commands, you increase your chances of passing the CCNA and CCNP exams greatly, and vastly improve your on-the-job skills. I recommend you visit http://www.cisco.com/univercd for more show and debug commands. Learning to negotiate this valuable online resource will truly help you become more valuable on the job. Every Cisco router and switch command, along with default and usage guidelines, can be found on this site. I'll have an article posted soon to help you learn your way around the site; in the meantime, I urge you to begin adding this website to your troubleshooting toolkit. Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of freeCCNA andCCNP tutorials, The Ultimate CCNA Study Package, and Ultimate CCNP Study Packages. For a FREE copy of his latest e-books, ,How To Pass The CCNA, and ,How To Pass The CCNP,, visit the website and download your free copies. You can also get FREE CCNA and CCNP exam questions every day! Pass theCCNA exam with The Bryant Advantage!
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