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Cisco CCNA Certification Exam Tutorial: ISDN Details You Must Know
By:Chris Bryant, CCIE #12933
CCNA exam success depends partially on knowing the details of ISDN, and there are plenty of them! To help you review for your CCNA exam, here are a few ISDN details that you must know on exam day. (They help in the real world, too – and there are still plenty of ISDN networks out there!
The Cisco-proprietary version of HDLC is the default encapsulation type for serial and ISDN interfaces.
R2#show interface serial0
Serial0 is up, line protocol is up
Hardware is HD64570
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255
Encapsulation HDLC, loopback not set, keepalive set (10 sec)
While there’s only one D-channel in BRI, PRI (US) and PRI (EU), the bandwidth of that D-channel does vary from BRI to PRI. It’s 16 kbps in BRI and 64 kbps in both PRI versions.
The global command isdn switch-type must be configured before you can even begin to have ISDN work. show isdn status will tell you whether or not you’ve done this correctly.
R2#show isdn status
**** No Global ISDN Switchtype currently defined ****
ISDN BRI0 interface
dsl 0, interface ISDN Switchtype = none
Layer 1 Status:
DEACTIVATED
Layer 2 Status:
Layer 2 NOT Activated
Layer 3 Status:
0 Active Layer 3 Call(s)
PAP allows passwords to be different; CHAP requires that they be the same.
PAP requires the “ppp pap sent-username” interface-level command. CHAP has no equivalent command.
Define interesting traffic with dialer-list and link that list to the interface with dialer-group.
R2#conf t
R2(config)#dialer-list 1 proto ip permit
R2(config)#int bri0
R2(config-if)#dialer-group 1
The dialer idle-timeout value is expressed in seconds, not minutes. (Even IOS Help isn’t totally clear on this.)
R2(config)#int bri0
R2(config-if)#dialer-group 1
R2(config-if)#dialer idle-timeout ?
<1-2147483> Idle timeout before disconnecting a call
R2(config-if)#dialer idle-timeout 120
Dialer map maps a remote IP address to a remote phone number. You never dial the local router’s phone number.
dialer load-threshold requires the ppp multilink command to be configured, and the value of dialer load-threshold is expressed as a ratio of 255, NOT 100. For example, if you want the second b-channel to come up when the first reaches 50% of capacity, the value to express with dialer load-threshold would be 50% of 255 – which equals 127.
R2(config)#int bri0
R2(config-if)#encap ppp
R2(config-if)#ppp multilink
R2(config-if)#dialer load-threshold ?
<1-255> Load threshold to place another call
Success on the CCNA exam depends on knowing the details. Keep studying, keep practicing on real Cisco routers and switches, keep a positive attitude, and you're on your way to CCNA exam success!
Article Source: http://www.dailynewarticles.com
Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of free CCNA and CCNP tutorials, The Ultimate CCNA Study Package, and Ultimate CCNP Study Packages.
You can also join his RSS feed and visit his blog, which is updated several times daily with new Cisco certification articles, free tutorials, and daily CCNA / CCNP exam questions! Details are on the website.
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! Get your CCNA study guide from The Bryant Advantage!
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