debug ppp negotiation

Answered Question
Mar 29th, 2009

Hi every body!

I was reading about PPP which is suite of protocols. One of the protocol is LCP

According to my book, LCp is charged with establishing, maintaining and terminating the link.

Curious , i set up small lab as r1----r2

and use " debug ppp negotiation " on r2 to see what parameters are negotiated as the link is brought up.

Below is the output:

LINK-3-UPDOWN: Interface Serial0, changed state to up

Se0 PPP: Treating connection as a dedicated line

Se0 PPP: Phase is ESTABLISHING, Active Open

Se0 LCP: O CONFREQ [Closed] id 90 len 15

Se0 LCP: AuthProto CHAP (0x0305C22305)

Se0 LCP: MagicNumber 0x10AF116C (0x050610AF116C)

Se0 LCP: I CONFACK [REQsent] id 90 len 15

Se0 LCP: AuthProto CHAP (0x0305C22305)

Se0 LCP: MagicNumber 0x10AF116C (0x050610AF116C)

Se0 LCP: TIMEout: Time 0x33E2CC State ACKrcvd

Se0 LCP: O CONFREQ [ACKrcvd] id 91 len 15

Se0 LCP: AuthProto CHAP (0x0305C22305)

Se0 LCP: MagicNumber 0x10AF116C (0x050610AF116C)

Se0 LCP: I CONFACK [REQsent] id 91 len 15

Se0 LCP: AuthProto CHAP (0x0305C22305)

Se0 LCP: MagicNumber 0x10AF116C (0x050610AF116C)

Se0 LCP: TIMEout: Time 0x33EAC4 State ACKrcvd

Se0 LCP: O CONFREQ [ACKrcvd] id 92 len 15

Se0 LCP: AuthProto CHAP (0x0305C22305)

Se0 LCP: MagicNumber 0x10AF116C (0x050610AF116C)

Se0 LCP: I CONFREQ [REQsent] id 2 len 10

Se0 LCP: MagicNumber 0x000CE809 (0x0506000CE809)

Se0 LCP: O CONFACK [REQsent] id 2 len 10

Se0 LCP: MagicNumber 0x000CE809 (0x0506000CE809)

Se0 LCP: I CONFACK [ACKsent] id 92 len 15

Se0 LCP: AuthProto CHAP (0x0305C22305)

Se0 LCP: MagicNumber 0x10AF116C (0x050610AF116C)

Se0 LCP: State is Open

Se0 PPP: Phase is AUTHENTICATING, by this end

Se0 CHAP: O CHALLENGE id 15 len 28 from "routerB"

Se0 CHAP: I CHALLENGE id 1 len 16 from "RouterA"

Se0 CHAP: Received Challenge but did not negotiate CHAP

Se0 CHAP: I RESPONSE id 15 len 28 from "RouterA"

Se0 CHAP: O SUCCESS id 15 len 4

Se0 PPP: Phase is UP

Se0 IPCP: O CONFREQ [Closed] id 15 len 10

Se0 IPCP: Address 198.198.198.34 (0x0306C6C6C622)

Se0 CDPCP: O CONFREQ [Closed] id 5 len 4

Se0 LCP: I PROTREJ [Open] id 3 len 10 protocol CDPCP (0x820701050004)

Se0 CDPCP: State is Closed

%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0, changed state to up

Se0 PPP: Unsupported or un-negotiated protocol. Link cdp

Se0 PPP: Trying to negotiate NCP for Link cdp

Se0 CDPCP: State is Closed

Se0 CDPCP: TIMEout: Time 0x33EEC1 State Closed

Se0 CDPCP: State is Listen

Se0 IPCP: TIMEout: Time 0x33F4E4 State REQsent

Se0 IPCP: O CONFREQ [REQsent] id 16 len 10

Se0 IPCP: Address 198.198.198.34 (0x0306C6C6C622)

routerB#

Se0 IPCP: TIMEout: Time 0x33FE64 State REQsent

Se0 IPCP: O CONFREQ [REQsent] id 17 len 10

Se0 IPCP: Address 198.198.198.34 (0x0306C6C6C622)

routerB#

Se0 IPCP: TIMEout: Time 0x340638 State REQsent

Se0 IPCP: O CONFREQ [REQsent] id 18 len 10

Se0 IPCP: Address 198.198.198.34 (0x0306C6C6C622)

routerB#

routerB#

routerB#

Se0 IPCP: TIMEout: Time 0x340E0C State REQsent

Se0 IPCP: O CONFREQ [REQsent] id 19 len 10

Se0 IPCP: Address 198.198.198.34 (0x0306C6C6C622)

routerB#

routerB#

Se0 CHAP: I CHALLENGE id 2 len 16 from "RouterA"

Se0 CHAP: Received Challenge but did not negotiate CHAP

============================

All i can see magic numbers, which ensures the link is not looped. what others things are negotiated while the link is being established besides the authentication method ?

thanks a lot!

I have this problem too.
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Correct Answer by Edison Ortiz about 7 years 8 months ago

My question is during link link establishing phase, LCP negotiates some parameters , besides some check such as loop detection, what are those parameters? One of the parameter is authentication method but i am just wondering about what are other parameters ?

Hope this link helps:

http://www.tcpipguide.com/free/t_PPPLinkControlProtocolLCPFrameFormats.htm

__

Edison.

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Edison Ortiz Mon, 03/30/2009 - 06:54

. what others things are negotiated while the link is being established besides the authentication method ?

username and password?

__

Edison.

sarahr202 Mon, 03/30/2009 - 08:19

Thanks a lot Edison!

I believe user name and password are exchanged in authentication phase which follows the link establishment phase. I might be wrong but that is what the book shows.

Edison Ortiz Mon, 03/30/2009 - 08:24

Sarah,

You are right, I guess I didn't understand your question.

You asked 'what other things are negotiated' and other than the authentication method, that will be the credentials.

What exactly are you looking for?

__

Edison.

sarahr202 Mon, 03/30/2009 - 09:02

Thanks a lot Edison for being so patient with me.

I was reading about ppp prtocol suite. One of the protocol is LCP. My book says LCP job is to establish and terminate link. Book also mentions that before Lcp establishes a link, it negotiates some parameters , perform some checks such as loop detection etc.

Book shows a illustration which makes me feel during link establishing phase, lcp also negotiates which authentication method the ppp peer will use.After the link is established, authentication phase begins.

My question is during link link establishing phase, LCP negotiates some parameters , besides some check such as loop detection, what are those parameters? One of the parameter is authentication method but i am just wondering about what are other parameters ?

Thanks a lot!

Correct Answer
Edison Ortiz Mon, 03/30/2009 - 10:45

My question is during link link establishing phase, LCP negotiates some parameters , besides some check such as loop detection, what are those parameters? One of the parameter is authentication method but i am just wondering about what are other parameters ?

Hope this link helps:

http://www.tcpipguide.com/free/t_PPPLinkControlProtocolLCPFrameFormats.htm

__

Edison.

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