weird PPP CHAP authentication problem

[GeneralZod]

Hi all.

I have a weird PPP CHAP problem and was wondering whether anyone could help me. Basically I’m trying to connect a Cisco 1841 to a DSL circuit provided by Claranet inthe UK. The problem is that the router fails to authenticate thus the circuit never comes up [Vi2 is in up/down state]. Now here is the interesting part, if I copy the config [see below] from the 1841 and paste it on a 837 the 837 can authenticate successfully and I am able to use the circuit fine.

I also checked the WIC-1-DSL chipset and noise levels and all seems to be fine on both routers. Could this problem be related to an IOS issue?

Thanks in advance

config:

!
interface Loopback100
ip address 212.169.1.23 255.255.255.255
!
interface ATM0
bandwidth 288
no ip address
no ip redirects
no ip unreachables
no ip proxy-arp
load-interval 30
no atm ilmi-keepalive
dsl operating-mode auto
!
interface ATM0.1 point-to-point
bandwidth 512
pvc 0/38
pppoe-client dial-pool-number 1
!
!
interface Dialer1
bandwidth 512
ip unnumbered Loopback100
encapsulation ppp
no ip route-cache cef
no ip route-cache
dialer pool 1
dialer-group 1
no cdp enable
ppp chap hostname xxxxx
ppp chap password xxxxx
!

 

[helpdeskdan]

That does indeed seem odd. Have you done a debug ppp authentication?

 

[GeneralZod]

Hi, yes I have and I keep getting the 'PPP authentiation required' message in the logs.

 

[S3M1N0L3]

I'm not too familiar with DSL connections but

Can you post your sho int for this.
Is the 837 provided by the ISP? I only ask in case they have something in place to stop other forms of CPE being added to the ckt.

I see ppoe and chap. Those are two separate forms of authentication I believe. If so, is ppoe authenticating? (I'm also not too familiar with that and forgive my ignorance but I don't see a login and password for ppoe).

Also, if you think it's an authentication issue, have you run a debug to see if that's the case and not something lower on the OSI that is causing this? There may also be logs indicating what the issue is. Posting those would be helpful as well.

Really, I don't know too much about this setup but I didn't want your issue to go without a response and those are the things that I would check.

 

[helpdeskdan]

Well, not exactly; it is pppoe - ppp over ethernet. Chap is a form of authentication ppp uses, pppoe is a way of encapsulating ppp so it runs over ethernet. Post the output of debug ppp auth.

 

[S3M1N0L3]

Makes sense.. Thanks

 

[KiscoKid]

It is not valid to have a part pppoe configuration when you using pppoa (as this is the only DSL technology BT support curently). Therefore can I suggest you make the following amendments:

interface ATM0.1 point-to-point
bandwidth 512
pvc 0/38
encapsulation aal5mux ppp dialer
dialer pool-member 1

interface Dialer1
ppp authentication chap callin

 

[GeneralZod]

I just realised I posted the wrong config. [Thanks for correcting the error]. Here is the correct one.

!
interface Loopback100
description GRE Tunnel Source address
ip address 212.169.1.132 255.255.255.255
!
interface Ethernet0
no ip address
hold-queue 100 out
!
interface ATM0
bandwidth 288
no ip address
load-interval 30
no atm ilmi-keepalive
pvc 0/38
encapsulation aal5mux ppp dialer
dialer pool-member 1
!
dsl operating-mode auto
!

!
interface Dialer1
bandwidth 512
ip unnumbered Loopback100
no ip unreachables
encapsulation ppp
dialer pool 1
dialer-group 1
no cdp enable
ppp chap hostname xxxx
ppp chap password xxxx
!
ip classless
ip route 0.0.0.0 0.0.0.0 Dialer1

 

[GeneralZod]

Oh, I'll try and get the debugs.