cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
1177
Views
5
Helpful
7
Replies

Problem with ppp authentication chap

Searon
Level 1
Level 1

Dear Cisco Community,

 

It's weird but the moment I do ppp authentication chap I get that my serial link goes down, I have no idea how to fix it none of the solutions I find on google work...

 

%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0/0, changed state to down

 

ip adresses are set correct aswell

 

Anyone have an idea what I forget?

 

ip route 0.0.0.0 0.0.0.0 193.190.239.1

brussel(config)#username brussel password cisco

brussel(config)#

brussel(config)#int s0/0/0

brussel(config-if)#

brussel(config-if)#enc

brussel(config-if)#encapsulation ppp

brussel(config-if)#ppp authentication chap

 

ip route 0.0.0.0 0.0.0.0 193.190.239.2

isp-1(config)#username isp-1 password cisco

isp-1(config)#

isp-1(config)#int s0/0/0

isp-1(config-if)#encapsulation ppp

isp-1(config-if)#ppp authentication chap

 

Also hostname is same as the username

1 Accepted Solution

Accepted Solutions

Hello,

 

you need to configure the username of the peer. Make sure the configs look like below:

 

brussel

 

username isp-1 password cisco
!
int s0/0/0
encapsulation ppp
clock rate 64000
ppp authentication chap

 

 

isp-1

 

username brussel password cisco
!
int s0/0/0
encapsulation ppp
ppp authentication chap

View solution in original post

7 Replies 7

Hello,

 

you need to configure the username of the peer. Make sure the configs look like below:

 

brussel

 

username isp-1 password cisco
!
int s0/0/0
encapsulation ppp
clock rate 64000
ppp authentication chap

 

 

isp-1

 

username brussel password cisco
!
int s0/0/0
encapsulation ppp
ppp authentication chap

I tried but the moment I give in "ppp authentication chap" the interface goes down and configuring it on the other router doesn't bring it up like it should..

 

temp1.png

Hello,

 

reload both routers and post the output of 'sh run'. From the output you have posted, it looks like on the isp-1 router you have entered the username twice, with different passwords ?

Hello @Searon ,

be very careful when you type the username commands.

We see from your screenshot that you type twice with the first time the password is cisco and the second time is "cisco !" ?

 

The two passwords must match.

 

You can use the following commands to debug

debug ppp negotiation

debug ppp authentication

terminal monitor

 

However, you may have an even more basic issue at OSI layer 1 because the router on the left does not accept the clock rate command and the router on the right has no clock rate command .

But this can be not an issue in packet tracer if it behaves like GNS3. In real world one side should give the clock as this is a synchronous serial line.

 

Hope to help

Giuseppe

 

Oh, now it works! I removed the previous login, but it seems you need to configure both username and passwords on both routers! The moment I added username brussel password cisco back to the router brussel the line went on again!

Hello @Searon ,

you are right it is a mutual authentication using locally defined username/password pairs so both username must be defined on both routers.

 

Hope to help

Giuseppe

 

Hello

You could also use unidirectional authtentication so then you would not require both usernames on each host.

brussel
username isp-1 password cisco

int s0/0/0
encapsulation ppp
clock rate 64000
ppp authentication chap callin < one way authentication
ppp chap hostname brussel

 

isp-1
username brussel password cisco
int s0/0/0
encapsulation ppp
ppp chap hostname  isp-1

 

or two way authentication both rtrs.
int x/x
no ppp chap hostname xxx
ppp authentication chap callin


Please rate and mark as an accepted solution if you have found any of the information provided useful.
This then could assist others on these forums to find a valuable answer and broadens the community’s global network.

Kind Regards
Paul
Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: