As soon as I turned ppp off, the line came up

[JoshGarmonCiscoCCNA]

I just had a weird and annoying experience.

Two Routers for my class lab, correct configurations on BOTH ends (same subnet, both no shut, same encapsulation type, same authentication type, correct usernames and passwords)...line STILL refused to come up until I finally just turned ppp off altogether.

What was the reason for this?

R1

username R2 password ciscoppp

int ser 0/0/0

ip address 191.0.5.8 255.255.255.224

encapsulation ppp

ppp authentication pap

no shut

R2

username R1 password ciscoppp

int ser 0/0/0

ip address 191.0.5.19 255.255.255.224

encapsulatoin ppp

ppp authentcation pap

no shut

[Georg Pauwen]

Hello,

for PAP authentication, you need to add the following line to both router's interfaces:

R1(config-if)# ppp pap sent-username R1 password ciscoppp

R2(config-if)# ppp pap sent-username R2 password ciscoppp

[JoshGarmonCiscoCCNA]

Hmm,

I've never seen those commands in my life before, are they new?

It has ALWAYS worked for me the way I just configured it, always.

Could it be an IOS/Hardware difference between the two Routers?

That's the only reason I can think for why this was not working.

[Georg Pauwen]

Josh, if anything, that command is rather old, so it might have become obsolete in newer versions. Does applying it bring your connection up ?

[JoshGarmonCiscoCCNA]

Hello

I tried this again in Packet Tracer and yes I applied those "sent username" commands and it worked.

However, I took them off and it was STILL working.

I don't know if it's just the Routers taking too long for the original commands to finally kick in or what.

I've never seen this "sent username" commands in my life.

I'm very confused.

[Georg Pauwen]

Josh,

I have Packet Tracer, which devices have you connected (which router types) ? I think they are all running on 12.x versions. The 'sent username' command was part of my CCIE study...in 2002 ! That is why I remembered it...

Either way, tell me which routers you are using in Packet Tracer, and I'll try and lab it...

[JoshGarmonCiscoCCNA]

I used a 1941 and an 819 with a Serial link.

PPP actually started working WITHOUT any authentication type.

Just merely configuring encapsulation PPP on both ends, the link became open.

Very weird.

[JoshGarmonCiscoCCNA]

Hello

I still need an explanation for this, even to this day.

All of a sudden it's like neither PAP nor CHAP matter/work.

As soon as I turn either off on both sides...the Link finally works.

I am amazed.

Were changes made to PPP.

This is even happening in Packet Tracer.

I just experimented again.

I configured PPP on two Routers connected to each other with Serial interfaces, both in the correct subnet.

I configured the host/username/passwords appropriately.

I configured both with ppp authentication PAP and the link stayed down.

But as soon as I removed ANY authentication on them, the LINK CAME UP.

This is bizarre to me.

[Georg Pauwen]

Hello Josh,

odd. 

PPP authentication is optional, so I guess it makes sense that your link comes up when you remove it altogether.

With CHAP, the router by default uses its hostname to identify itself. So you need the hostname of the other router in the respective config, with identical passwords.

The 'ppp pap sent-username' is required for PAP, since otherwise the routers do not know who is sending the authentication request.

The configuration in your initial post, you say you got that working with PAP. It should only work with CHAP. Weird. Can you debug ppp authentication and debug ppp negotiation ?

[JoshGarmonCiscoCCNA]

Yes it seems like I must have forgotten how PAP is configured.

I guess it's been too long.

PAP needs that 'sent username' part which I just totally lost memory of.

[JoshGarmonCiscoCCNA]

What about PAP with CHAP and vice versa?

[Georg Pauwen]

Josh,

the below is a working configuration. Doesn't really make sense, since PAP is first and then CHAP. I ma starting to get confused myself. You would expect that the 'sent username' is still required, but apparently it isn't...

R1#

username R2 password ciscoppp

interface Serial0/0
ip address 192.168.1.1 255.255.255.0
encapsulation ppp
ppp authentication pap chap

R2#

username R1 password ciscoppp

interface Serial0/0
ip address 192.168.1.2 255.255.255.0
encapsulation ppp
ppp authentication pap chap