120 Labs for Cisco CCNA 200-125 and CCENT Exams

Lab 96: PPP Authentication Using CHAP (Method #2)

Lab Objective:

The objective of this lab exercise is to configure two routers sharing a back-to-back Serial link encapsulated by PPP to authenticate each other using default CHAP parameters on Cisco IOS. By default, PPP connections are not authenticated or secured.

Lab Purpose:

PPP CHAP authentication configuration is a fundamental skill. One of the main reasons that PPP is so popular is because it has the capability to be secured and devices communicating using PPP can be authenticated. CHAP authentication is the most preferred method to secure PPP as it does not send usernames and passwords in clear text. As a Cisco engineer, as well as in the Cisco CCNA exam, you will be expected to know how to configure PPP CHAP authentication.

Certification Level:

This lab is suitable for CCNA certification exam preparation.

Lab Difficulty:

This lab has a difficulty rating of 6/10.

Readiness Assessment:

When you are ready for your certification exam, you should complete this lab in no more than 15 minutes.

Lab Topology:

Please use the following topology to complete this lab exercise:

Task 1:

Configure the hostnames on R1 and R2 as illustrated in the topology.

Task 2:

Enable the Serial interfaces on R1 and R2. The Serial0/0 interface on R2 is identified as the DCE in the topology. Use the appropriate show command to verify that this interface is indeed the DCE. Configure the DCE interface on R2 to provide clocking to R1. The clock speed should be 768 Kbps. Verify that R1 receives clocking information from R2.

Task 3:

Enable PPP encapsulation on R1 and R2 Serial0/0 interfaces. Configure IP addressing on R1 and R2 Serial0/0 interfaces as illustrated in the topology.

Task 4:

Verify your interface encapsulation, which should be PPP by default. Test connectivity between R1 and R2 by pinging between the routers.

Task 5:

Configure PPP CHAP authentication on R1 and R2. Configure R1 to use the CHAP username Router1 with the password MyPass. Configure R2 to use the CHAP username Router2 with the password MyPass.

Task 6:

Enable PPP authentication debugging on R1. Next, perform a shutdown command followed followed by a no shutdown command on Serial0/0. Verify that you see the two routers authenticating each other via PPP CHAP. Disable debugging when you are done.

Configuration and Verification

Task 1:

For reference information on configuring hostnames, please refer to earlier labs.

Task 2:

For reference information on verifying DTE/DCE status, please refer to earlier labs.

Task 3:

For reference information on enabling PPP encapsulation, please refer to earlier labs.

Task 4:

For reference information on verifying Serial encapsulation, please refer to earlier labs.

R1#ping 192.168.50.34 

Type escape sequence to abort. 
Sending 5, 100-byte ICMP Echos to 192.168.50.34, timeout is 2 seconds: 
!!!!! 
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms 

R2#ping 192.168.50.33 

Type escape sequence to abort. 
Sending 5, 100-byte ICMP Echos to 192.168.50.33, timeout is 2 seconds: 
!!!!! 
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms

Task 5:

R1#conf t 
Enter configuration commands, one per line.  End with CTRL/Z. 
R1(config)#int s0/0
R1(config-if)#ppp authentication chap 
R1(config-if)#ppp chap ? 
 hostname  Set alternate CHAP hostname 
 password  Set default CHAP password 
 refuse    Refuse to authenticate using CHAP 
 wait      Wait for caller to authenticate first 
R1(config-if)#ppp chap hostname Router1 
R1(config-if)#ppp chap password MyPass 
R1(config-if)#exit 
R1(config)#username Router2 password MyPass 
R1(config)#end 
R1# 

R2#configure ter 
Enter configuration commands, one per line.  End with CTRL/Z. 
R2(config)#interf ser0/0 
R2(config-if)#ppp authentication chap 
R2(config-if)#ppp chap hostname Router2 
R2(config-if)#ppp chap password MyPass 
R2(config-if)#exit 
R2(config)#username Router1 password MyPass 
R2(config)#end 
R2#

NOTE: By default, there is no need to configure a hostname to be used for CHAP authentication on Cisco IOS routers as they will use the hostname configured on the router. However, to use a different hostname, CHAP must be configured for that. This is performed using the ppp chap hostname and ppp chap password commands on the PPP interface used for CHAP authentication.

Task 6:

R2#debug ppp authentication 
PPP authentication debugging is on 
R2#config t
Enter configuration commands, one per line.  End with CTRL/Z. 
R2(config)#int s0/0 
R2(config-if)#shut 
*Mar  1 03:54:08.805: %LINK-5-CHANGED: Interface Serial0/0, changed state to administratively down 
*Mar  1 03:54:09.807: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0, changed state to down 
R2(config-if)#no shut 
*Mar  1 03:54:15.861: %LINK-3-UPDOWN: Interface Serial0/0, changed state to up 
*Mar  1 03:54:15.861: Se0/0 PPP: Using default call direction 
*Mar  1 03:54:15.861: Se0/0 PPP: Treating connection as a dedicated line 
*Mar  1 03:54:15.861: Se0/0 PPP: Session handle[D50000E3] Session id[229] 
*Mar  1 03:54:15.861: Se0/0 PPP: Authorization required 
*Mar  1 03:54:15.869: Se0/0 CHAP: O CHALLENGE id 181 len 28 from “Router2” 
*Mar  1 03:54:15.869: Se0/0 CHAP: I CHALLENGE id 181 len 28 from “Router1” 
*Mar  1 03:54:15.873: Se0/0 CHAP: Using hostname from interface CHAP 
*Mar  1 03:54:15.877: Se0/0 CHAP: Using password from AAA 
*Mar  1 03:54:15.877: Se0/0 CHAP: O RESPONSE id 181 len 28 from “Router2” 
*Mar  1 03:54:15.877: Se0/0 CHAP: I RESPONSE id 181 len 28 from “Router1” 
*Mar  1 03:54:15.881: Se0/0 PPP: Sent CHAP LOGIN Request 
*Mar  1 03:54:15.881: Se0/0 PPP: Received LOGIN Response PASS 
*Mar  1 03:54:15.885: Se0/0 PPP: Sent LCP AUTHOR Request 
*Mar  1 03:54:15.885: Se0/0 PPP: Sent IPCP AUTHOR Request 
*Mar  1 03:54:15.885: Se0/0 CHAP: I SUCCESS id 181 len 4 
*Mar  1 03:54:15.889: Se0/0 LCP: Received AAA AUTHOR Response PASS 
*Mar  1 03:54:15.889: Se0/0 IPCP: Received AAA AUTHOR Response PASS 
*Mar  1 03:54:15.889: Se0/0 CHAP: O SUCCESS id 181 len 4 
*Mar  1 03:54:15.893: Se0/0 PPP: Sent CDPCP AUTHOR Request 
*Mar  1 03:54:15.897: Se0/0 PPP: Sent IPCP AUTHOR Request 
*Mar  1 03:54:15.897: Se0/0 CDPCP: Received AAA AUTHOR Response PASS 
*Mar  1 03:54:16.895: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0, changed state to up 
R2(config-if)#end 
R2#
*Mar  1 03:54:21.114: %SYS-5-CONFIG_I: Configured from console by console 
R2#undebug ppp authentication 
PPP authentication debugging is off 
R2#

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