Cisco CCNA CCNP Exam Tutorial Testing ISDN Links Without Pings

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Cisco CCNA / CCNP Exam Tutorial: Testing ISDN Links Without Pings


Summary:

While using pings to test ISDN links is common, there are more effective methods to ensure your ISDN link functions properly. Learn this essential technique from Chris Bryant, CCIE

12933.


Article:


To achieve Cisco CCNA and CCNP certifications, mastering ISDN is crucial. Despite some beliefs, ISDN remains widely used and requires ongoing support. Troubleshooting ISDN involves several considerations: Is the correct switch type set? Are the dialer map statements accurate? Have the dialer-group and dialer-list commands been configured correctly? These are just the beginning.

I always emphasize that troubleshooting begins at Layer 1, the Physical layer of the OSI model. Typically, ISDN troubleshooting involves sending pings across the link, but it's possible to test connections without pings or even before assigning IP addresses to the BRI interfaces.

Conducting test calls before configuring the interfaces is beneficial, as it confirms a valid connection before you proceed with detailed configurations (and ISDN requires a lot of setup!).

To place a test call without pings, utilize the `isdn call interface` command:

```plaintext
R1

isdn call interface bri0 8358662

R1#
03:54:43: BR0 DDR: Attempting to dial 8358662
03:54:43: %LINK-3-UPDOWN: Interface BRI0:1, changed state to up
03:54:44: BR0:1 DDR: dialer protocol up
03:54:45: %LINEPROTO-5-UPDOWN: Line protocol on Interface BRI0:1, changed state to up
03:54:49: %ISDN-6-CONNECT: Interface BRI0:1 is now connected to 8358662 R2
```

To disconnect the test call properly, use the `isdn disconnect interface` command, and IOS Help will show the available options:

```plaintext
R1

isdn disconnect interface bri 0 ?

all Disconnect the data call(s) on all b channels
b1 Disconnect the data call on b1 channel
b2 Disconnect the data call on b2 channel
R1

isdn disconnect interface bri 0 all

03:58:36: BR0:1 DDR: disconnecting call
03:58:36: BR0:2 DDR: disconnecting call
03:58:36: %ISDN-6-DISCONNECT: Interface BRI0:1 disconnected from 8358662 R2, call lasted 20 seconds
03:58:36: %LINK-3-UPDOWN: Interface BRI0:1, changed state to down
03:58:36: BR0:1 DDR: disconnecting call
03:58:37: %LINEPROTO-5-UPDOWN: Line protocol on Interface BRI0:1, changed state to down
```

Disconnecting correctly is essential because abruptly shutting an ISDN call, whether a test or genuine, is discouraged. Telcos and ISDN lab devices prefer orderly disconnections?"always let the d-channel handle the disconnection process rather than merely shutting down the interface.

You can find the original non-AI version of this article here: Cisco CCNA CCNP Exam Tutorial Testing ISDN Links Without Pings.

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