To earn your Cisco CCNA and CCNP certifications, you've got to master ISDN - and in spite of what some people say, there's nevertheless a lot of ISDN out there that needs to be supported. And when it comes to troubleshooting ISDN, there's a lot to appear at. Is the appropriate ISDN switchtype configured? Are the dialer map statements right? What about the dialer-group and dialer-list commands? And that's just the start off.
I usually say that all troubleshooting begins at Layer 1, the Physical layer of the OSI model. The usual strategy of troubleshooting ISDN is sending pings across the hyperlink, but the connection can be tested with out using pings or even before assigning IP addresses to the BRI interfaces!
It's a very good notion to place these test calls ahead of configuring the interfaces - that way, you know you've got a valid connection prior to starting the configuration (and there's a lot of config to go along with ISDN!)
To location a test contact with out utilizing pings, use the isdn call interface command.
R1#isdn call interface bri0 8358662
R1#
03:54:43: BR0 DDR: Attempting to dial 8358662
03:54:43: %Hyperlink-3-UPDOWN: Interface BRI0:1, changed state to up
03:54:44: BR0:1 DDR: dialer protocol up
03:54:45: %LINEPROTO-five-UPDOWN: Line protocol on Interface BRI0:1, changed state to up
03:54:49: %ISDN-six-CONNECT: Interface BRI0:1 is now connected to 8358662 R2
To tear the test contact down correctly, use isdn disconnect interface. IOS Aid displays the options with this command.
R1#isdn disconnect interface bri ?
all Disconnect the data get in touch with(s) on all b channels
b1 Disconnect the information call on b1 channel
b2 Disconnect the information contact on b2 channel
R1#isdn disconnect interface bri all
03:58:36: BR0:1 DDR: disconnecting call
03:58:36: BR0:two DDR: disconnecting contact
03:58:36: %ISDN-6-DISCONNECT: Interface BRI0:1 disconnected from 8358662
R2, contact lasted 20 seconds
03:58:36: %Hyperlink-three-UPDOWN: Interface BRI0:1, changed state to down
03:58:36: BR0:1 DDR: disconnecting contact
03:58:37: %LINEPROTO-5-UPDOWN: Line protocol on Interface BRI0:1, changed state to down
I say "correctly" since the one point you don't want to do to finish an ISDN contact, test or otherwise, is just shut the interface. Telcos don't like it, and ISDN lab devices like it even much less. Always let the d-channel do its function and tear the call down in an orderly style - don't just cut it off by shutting the interface down.
Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, house of more than 100 free certification exam tutorials, such as Cisco CCNA certification test prep articles. His exclusive Cisco CCNA study guide and Cisco CCNA education is also accessible!
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