Cisco CCNA CCNP Certification Exam Tutorial Configuring PPP Callback
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Cisco CCNA/CCNP Certification Exam Tutorial: Configuring PPP Callback
Summary
Mastering PPP Callback configuration is crucial for success in the Cisco CCNA and CCNP exams, and it plays a significant role in real-world networks. Chris Bryant, CCIE
12933, explains how and why to implement PPP Callback.
Understanding PPP Callback
In certain scenarios, a remote router needs to dial into a central router, potentially incurring high toll charges. PPP Callback helps manage these costs by allowing the callback server to take responsibility for the call charges. Here's how it works: The client initiates a call to the server for authentication, then the server hangs up and calls the client back, ensuring the client avoids call charges.
Example Setup
Let's consider a setup where R2 is the client and R1 acts as the callback server. Below are the configurations needed for both.
Client Configuration (R2)
```plaintext
username R1 password CCIE
interface BRI0
ip address 172.12.12.2 255.255.255.0
encapsulation ppp
dialer map ip 172.12.12.1 name R1 broadcast 5557777
dialer-group 1
isdn switch-type basic-ni
ppp callback request
ppp authentication chap
```
The `ppp callback request` command is key, allowing the interface to request a callback.
Server Configuration (R1)
```plaintext
username R2 password CCIE
interface BRI0
ip address 172.12.12.1 255.255.255.0
encapsulation ppp
dialer callback-secure
dialer map ip 172.12.12.2 name R2 class CALL_R2_BACK broadcast 5558888
dialer-group 1
isdn switch-type basic-ni
ppp callback accept
ppp authentication chap
map-class dialer CALL_R2_BACK
dialer callback-server username
```
Key Server Configurations:
- `dialer callback-secure`: Ensures secure callback, disconnecting if authentication fails.
- `ppp callback accept`: Enables PPP callback on the server.
- `dialer callback-server username`: Identifies the callback client.
Testing Connectivity
Let's test the setup by sending a ping from R2 to R1 to trigger the callback.
```plaintext
R2
ping 172.12.12.1
```During the ping sequence, you'll observe the dialing process:
- The client dials and disconnects after negotiating a callback.
- The server then calls the client back, confirming the callback's success.
Example output from R2:
```plaintext
02:45:42: BR0 DDR: Dialing cause ip (s=172.12.12.2, d=172.12.12.1)
02:45:42: BR0:1 DDR: Callback negotiated - Disconnecting now
02:45:57: BR0:1 DDR: Callback received from R1 5557777
```
This output shows the successful negotiation and completion of PPP Callback.
Conclusion
The PPP Callback function, as demonstrated, not only aids in CCNA and CCNP exam preparation but also offers practical benefits by reducing call costs in real networks. By understanding and configuring PPP Callback, networks can achieve greater efficiency and cost savings.
You can find the original non-AI version of this article here: Cisco CCNA CCNP Certification Exam Tutorial Configuring PPP Callback.
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