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