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 theres only one D-channel in BRI, PRI (US) and PRI (EU), the bandwidth of that D-channel does vary from BRI to PRI. Its 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 youve 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 isnt 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 routers 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! |
