Cisco CCNA CCNP Certification Exam Caller ID Screening And Callback
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Cisco CCNA/CCNP Certification Exam: Caller ID Screening and Callback
Summary
To excel in Cisco certification exams like CCNA and CCNP, it's crucial to master multiple techniques. Let's explore an alternative method for configuring ISDN callback.
Understanding Caller ID Screening and Callback
Aspiring CCNA and CCNP professionals should know how Cisco router features can optimize client operations. For instance, if a remote site has higher toll charges than a central hub, configuring the hub to disconnect and call back the remote site can save costs and impress clients.
While PPP callback is common, it's beneficial to be familiar with other methods. One such technique is Caller ID Screening and Callback. Let's delve into how these work.
What is Caller ID Screening?
Often, "Caller ID" is associated with displaying incoming call numbers. However, on a Cisco router, Caller ID Screening acts as a security measure, specifying which phone numbers can connect to the router.
Using the `isdn caller` command, you can create a list of authorized numbers. This command supports wildcards; for example, `isdn caller 555xxxx` authorizes any 7-digit number starting with 555. In our setup, we'll configure R2 with this command and observe the results using `debug dialer` on R1 during a ping.
Configuration Example:
```shell
R2(config-if)
isdn caller 555xxxx
R1debug dialer
R1ping 172.12.12.2
```After executing the ping, R1 doesn’t provide immediate troubleshooting hints, but checking R2 with `show dialer` reveals which calls were screened.
Implementing Caller ID Callback
To enable R2 to disconnect and call back R1, use the callback feature:
```shell
R2(config-if)
isdn caller 8358661 callback
```When R1 pings R2, the ping fails initially. However, R2 subsequently calls R1 back, showcasing the callback functionality effectively.
Callback Example:
```shell
R1
ping 172.12.12.2
No initial success, but callback follows
R2show dialer
```This command confirms the callback, showing the dialer state as a callback return call.
Considerations
It's important to note that not all telecom switches support Caller ID Callback. Where feasible, PPP Callback might be a more reliable option. Nevertheless, knowing multiple techniques is advantageous in Cisco configurations.
Conclusion
In Cisco exams, flexibility and comprehensive understanding of routing techniques are key. By mastering alternatives like Caller ID Screening and Callback, you can enhance your problem-solving toolkit and potentially save clients money.
Keep practicing various methods to build robust networking skills!
You can find the original non-AI version of this article here: Cisco CCNA CCNP Certification Exam Caller ID Screening And Callback.
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