how to configure hdlc ppp pap chap step by step guide and example

	how to configure hdlc ppp pap chap step by step guide and example

Configure hdlc ppp pap chap

In this article I will demonstrate how can you configure wan encapsulation protocols. HDLC is the default encapsulation for synchronous serial links on Cisco routers. You would only use the encapsulation hdlc command to return the link to its default state

For practical example of HDLC PPP create a simple topology as shown in figure or download this pre configured topology and load it in packet tracer.

Pre configured topology for PPP and HDLC
configure hdlc

Double click on R1 and check the default encapsulation

Router> Router#show interfaces serial 0/0/0 Serial0/0/0 is up, line protocol is up (connected) Hardware is HD64570 Internet address is 20.0.0.1/8 MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec, rely 255/255, load 1/255 Encapsulation HDLC, loopback not set, keepalive set (10 sec) [output is omited]

As you can verify that default encapsulation on router is HDLC. A wan link work only when it detects same protocols on same sides. To check it change the default encapsulation to PPP.

Router#configure terminal Router(config)#interface serial 0/0/0 Router(config-if)#encapsulation ppp Router(config)#exit Router#show interfaces serial 0/0/0 Serial0/0/0 is up, line protocol is down (disabled) Hardware is HD64570 Internet address is 20.0.0.1/8 MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec, rely 255/255, load 1/255 Encapsulation PPP, loopback not set, keepalive set (10 sec) [output is omited]

as you can see that line protocols is disable. To enable it set the encapsulation back to HDLC and restart the port with shut down command

Router#configure terminal Router(config)#interface serial 0/0/0 Router(config-if)#encapsulation hdlc Router(config-if)#shutdown Router(config-if)#no shutdown Router(config-if)#exit Router(config)#exit Router#show interfaces serial 0/0/0 Serial0/0/0 is up, line protocol is up (connected) Hardware is HD64570 Internet address is 20.0.0.1/8 MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec, rely 255/255, load 1/255 Encapsulation HDLC, loopback not set, keepalive set (10 sec) [output is omited]

Configuration of PPP

Now we will configure PPP encapsulations on both router. We will also authenticate it with CHAP. Hostname of Router are R1 and R2 and password is vinita.

Double Click on R1 and configure it

Router>enable Router#configure terminal Router(config)#hostname R1 R1(config)#username R2 password vinita R1(config)#interface serial 0/0/0 R1(config-if)#encapsulation ppp R1(config-if)#ppp authentication chap R1(config-if)#exit R1(config)#

Now configure R2 for PPP

Router>enable Router#configure terminal Router(config)#hostname R2 R2(config)#username R1 password vinita R2(config)#interface serial 0/0/0 R2(config-if)#encapsulation ppp R2(config-if)#ppp authentication chap R2(config-if)#exit %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0/0, changed state to up R2(config)#

HDLC PPP command reference sheet

*Router(config)#interface serial 0/0/0*	Moves to interface configuration mode
*Router(config-if)#encapsulation hdlc*	Sets the encapsulation mode for this interface to HDLC
*Router(config)#interface serial 0/0/0*	Moves to interface configuration mode
*Router(config-if)#encapsulation ppp*	Changes encapsulation from default HDLC to PPP
*Router(config)#username R1 password vinita*	Sets a username of R1 and a password of vinita for authentication from the other side of the PPP serial link. This is used by the local router to authenticate the PPP peer
*Router(config)#interface serial 0/0/0*	Moves to interface configuration mode.
*Router(config-if)#ppp authentication pap*	Turns on Password Authentication Protocol (PAP) authentication only
*Router(config-if)#ppp authentication chap*	Turns on Challenge Handshake Authentication Protocol (CHAP) authentication only.
*Router(config-if)#ppp authentication pap chap*	Defines that the link will use PAP authentication, but will try CHAP if PAP fails or is rejected by other side.
*Router(config-if)#ppp authentication chap pap*	Defines that the link will use CHAP authentication, but will try PAP if CHAP fails or is rejected by other side.
*Router(config-if)#ppp pap sentusername R1 password vinita*	This command must be set if using PAP in Cisco IOS Software Release 11.1 or later
*Router#show interfaces serial x*	Lists information for serial interface x
*Router#show controllers serial x*	Tells you what type of cable (DCE/DTE) is plugged into your interface and whether a clock rate has been set
*Router#debug serial interface*	Displays whether serial keepalive counters are incrementing
*Router#debug ppp*	Displays any traffic related to PPP
*Router#debug ppp packet*	Displays PPP packets that are being sent and received
*Router#debug ppp negotiation*	Displays PPP packets related to the negotiation of the PPP link

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