Table of Contents
1. Introduction
2. Understanding PPP and Authentication
3. Configuring PPP on Router Interface
Step 1: Selecting the Interface
Step 2: Setting the Interface to PPP
Step 3: Optional Data Compression
Step 4: Optional PPP Quality
Step 5: Configuring PAP Authentication
Step 6: Configuring CHAP Authentication
Step 7: Optional PPP Multilink
Step 8: Resetting Interface to HDLC
4. Example Configuration
PAP Configuration Example
CHAP Configuration Example
5. Best Practices
6. Conclusion
1. Introduction
Point-to-Point Protocol (PPP) is a data link layer protocol commonly used to establish direct connections between two networking nodes. This guide will walk you through the process of configuring PPP with authentication on a Cisco router, covering both PAP (Password Authentication Protocol) and CHAP (Challenge Handshake Authentication Protocol).
2. Understanding PPP and Authentication
PPP supports two types of authentication:
- PAP (Password Authentication Protocol): A simple authentication protocol that sends the username and password in plain text.
- CHAP (Challenge Handshake Authentication Protocol): A more secure protocol that uses a three-way handshake to protect the authentication process.
3. Configuring PPP on Router Interface
To configure PPP with authentication, follow these steps:
Step 1: Selecting the Interface
First, select the interface you want to configure for PPP.
R1(config)# interface serial 0/0/0
Step 2: Setting the Interface to PPP
Set the interface encapsulation to PPP.
R1(config-if)# encapsulation ppp
Step 3: Optional Data Compression
Configure optional data compression if needed.
R1(config-if)# compress predictor
Step 4: Optional PPP Quality
Set a throughput threshold before the PPP link will reset. This is optional.
R1(config-if)# ppp quality 80
Step 5: Configuring PAP Authentication
To configure PAP authentication, use the following commands. Ensure the username and password match those sent by the other router.
R1(config)# username R-2 password PASSWORD
R1(config-if)# ppp authentication pap
R1(config-if)# ppp pap sent-username R-1 password PASSWORD
Step 6: Configuring CHAP Authentication
For CHAP authentication, the username must be the hostname of the other router, and the passwords must be the same on both routers.
R1(config)# username R-2 password PASSWORD
R1(config-if)# ppp authentication chap
Step 7: Optional PPP Multilink
If you need to combine multiple PPP links for more bandwidth, configure PPP multilink.
R1(config-if)# ppp multilink
Step 8: Resetting Interface to HDLC
To reset the interface back to its default HDLC encapsulation, use the following command.
R1(config-if)# encapsulation hdlc
4. Example Configuration
PAP Configuration Example
Here’s a complete example configuration for PAP authentication on Router R1:
R1(config)# username R-2 password PASSWORD
R1(config)# interface serial 0/0/0
R1(config-if)# encapsulation ppp
R1(config-if)# compress predictor
R1(config-if)# ppp quality 80
R1(config-if)# ppp authentication pap
R1(config-if)# ppp pap sent-username R-1 password PASSWORD
On Router R2, the configuration would be:
R2(config)# username R-1 password PASSWORD
R2(config)# interface serial 0/0/0
R2(config-if)# encapsulation ppp
R2(config-if)# ppp authentication pap
CHAP Configuration Example
Here’s a complete example configuration for CHAP authentication on Router R1:
R1(config)# username R-2 password PASSWORD
R1(config)# interface serial 0/0/0
R1(config-if)# encapsulation ppp
R1(config-if)# compress stac
R1(config-if)# ppp quality 80
R1(config-if)# ppp authentication chap
On Router R2, the configuration would be:
R2(config)# username R-1 password PASSWORD
R2(config)# interface serial 0/0/0
R2(config-if)# encapsulation ppp
R2(config-if)# ppp authentication chap
5. Best Practices
- Consistency: Ensure consistent configuration across all routers to avoid connectivity issues.
- Security: Prefer CHAP over PAP due to its more secure authentication mechanism.
- Documentation: Document all configurations for troubleshooting and maintenance purposes.
- Testing: Always test the configuration in a controlled environment before deployment.
6. Conclusion
Configuring PPP with authentication on a Cisco router is a straightforward process that enhances security and efficiency. By following this guide, you can ensure a reliable and secure PPP connection between your routers.
Feel free to reach out with any questions or comments about this configuration process!
