HDLC and PPP connections

HDLC

Cisco HDLC is enabled by default on serial interfaces.

//re-enable HDLC
R(config)#interface s0/3/0
R(config)#encapsulation hdlc

PPP

//enable and configure PPP encapsulation
R(config)#interface s0/3/0
R(config-if)#encapsulation ppp
R(config-if)#compress [predictor | stac]
R(config-if)#ppp quality 80     //if more than 20% packet loss, the link is taken down

//PPP multilink
R(config)#interface multilink 1
R(config-if)#ip address 10.0.0.1 255.255.255.0
R(config-if)#ppp multilink
R(config-if)#ppp multilink group 1
R(config)#interface s0/1/0
R(config-if)#no ip address
R(config-if)#encapsulation ppp
R(config-if)#ppp multilink
R(config-if)#ppp multilink group 1

//PPP PAP authentication
Usernames don’t have to match the router hostnames and passwords don’t have to be the same for both users.

Router1(config)#username R2 password cisco2
Router1(config-if)#ppp authentication pap
Router1(config-if)#ppp pap sent-username R1 password cisco1
Router2(config)#username R1 password cisco1
Router2(config-if)#ppp authentication pap
Router2(config-if)#ppp pap sent-username R2 password cisco2

//PPP CHAP authentication
Usernames are the router hostnames and passwords must be the same for both users.

R1(config)#username R2 password cisco
R1(config-if)#ppp authentication chap
R2(config)#username R1 password cisco
R2(config-if)#ppp authentication chap

Troubleshoot

R#show interfaces s0/3/0
R#show controllers s0/3/0
R#show ppp multilink
R#debug ppp

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