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[ScreenOS] Understanding PPP negotiation process with debugging logs.

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Article ID: KB22592 KB Last Updated: 06 Feb 2012Version: 2.0
Summary:
This article provides information about the PPP negotiation process, along with debugging logs.
Symptoms:
Environment:

Configuration of PPP is:
setppp profile "ISP"
setppp profile "ISP" static-ip
setppp profile "ISP" auth type pap
setppp profile "ISP" auth local-name "username"
setppp profile "ISP" auth secret "fzSzAn31N4Sbh/sukoCDLvhJEdn0DVK7vA=="
set interface "serial1/0" ppp profile ISP
set interface "serial1/0" encapppp
set interface serial1/0 hold-time up 10
set interface serial1/0 t3-options fcs 32
set interface serial1/0 t3-options compatibility-mode digital-link subrate 44.2Mb

Cause:

Solution:
The PPP process can be divided into the following stages:
  1. Outgoing links use UUCP, which facilitates incoming links to be auto-detected or require users to login to start the PPP shell. (UUCP UNIX -to- UNIX copy) is a set of programs and protocols that allow computers to communicate over serial connections, networks, or ordinary telephone lines. It supports two operations - file copying and remote command execution.

    ## 2011-05-24 19:56:01 : serial1/0 link state changed, new state 1
    ## 2011-05-24 19:56:01 : serial1/0, link changes from Down to Up
    ## 2011-05-24 19:56:01 : [PPPSEND]:(serial1/0) ppp_output:(ppp 0x7fb14e0/lolayer 0x7333e04): ppp_output_callback 0x5be6c0, sending len 18:
    ff:3:c0:21:1:ba:0:e:1:4:11:76:5:6:19:29:1d:c8:
    ## 2011-05-24 19:56:01 : SEND DECODE:(serial1/0) ***[LCP ConfReq <MRU 4470> <MAGIC 0x19291dc8>]***
    ## 2011-05-24 19:56:01 : serial1/0, LCP , fsm open, state : CLOSED -> REQSENT
    ## 2011-05-24 19:56:01 : serial1/0, ppp serial decap process the data pak, proto 0xc021

    ## 2011-05-24 19:56:01 : serial1/0, ppp control panel take the pak.
    ## 2011-05-24 19:56:01 : [PPPRECV]:(serial1/0) ppp_get_input:(ppp 0x7fb14e0/lolayer 0x7333e04): received len 18:
    ff:3:c0:21:1:a:0:e:1:4:11:76:5:6:9e:f6:74:f3:
    ## 2011-05-24 19:56:01 : RECV DECODE:(serial1/0) ***[LCP ConfReq <MRU 4470> <MAGIC 0x9ef674f3>]***
    ## 2011-05-24 19:56:01 : serial1/0 recv 0xc021 pak
    ## 2011-05-24 19:56:01 : code=2 nakloops=0 max=5
    ## 2011-05-24 19:56:01 : [PPPSEND]:(serial1/0) ppp_output:(ppp 0x7fb14e0/lolayer 0x7333e04): ppp_output_callback 0x5be6c0, sending len 18:

  2. Negotiate the MRU. The maximum size is up to 65,535 of the PPP frame; the default MRU is 1,500. If neither peer is changing the default, this option is not negotiated.

    ACCM (Asynchronous Control Character Map) - A bit map that enables (bit set to 1) or disables (bit set to 0) the use of character escapes for asynchronous links, for the 32 ASCII control characters from 0x00 to 0x20. By default, character escapes are used. The ACCM bit map is set to 0x00-00-00-00 for links with XON/XOFF software flow control).

    Magic number - A random number chosen to distinguish a peer and detect looped back lines.

    Field compression and multiple parameters - MRRU, SSN and endpoint discriminator.

  3. Authenticate the remote side of the link and/or supply the authentication information to the remote authenticator.

    ## 2011-05-24 19:56:01: serial1/0, ppp serial decap process the data pak, proto 0xc021
    ## 2011-05-24 19:56:01: serial1/0, ppp control panel take the pak.
    ## 2011-05-24 19:56:01: [PPPRECV]:(serial1/0) ppp_get_input:(ppp 0x7fb14e0/lolayer 0x7333e04): received len 18:
    ff:3:c0:21:2:ba:0:e:1:4:11:76:5:6:19:29:1d:c8:
    ## 2011-05-24 19:56:01: RECV DECODE:(serial1/0) ***[LCP ConfAck <MRU 4470> <MAGIC 0x19291dc8>]***
    ## 2011-05-24 19:56:01: serial1/0 recv 0xc021 pak
    ## 2011-05-24 19:56:01: serial1/0, LCP is UP
    ## 2011-05-24 19:56:01: lcp_up: *** LCP is up (ppp/f):(7fb14e0/7fb1f24) ***
    ## 2011-05-24 19:56:01: lcp_up: *** MRU: Local 4470, Remote MRU 4470, ***
    ## 2011-05-24 19:56:01: lcp_up: *** Magic: Local 0x19291dc8, Remote 0x9ef74014, ***
    ## 2011-05-24 19:56:01: lcp_up: *** AsyncMap: Local 0x0, Remote 0x0, ***
    ## 2011-05-24 19:56:01: lcp_up: *** Auth as Client via NON auth ***
    ## 2011-05-24 19:56:01: serial1/0, link_established: ppp 0x7fb14e0, ppp->lolayer 0x7333e04, Entered, auth_req 0, go->neg_chap 0, go->neg_upap 0
    ## 2011-05-24 19:56:01: network_phase: Entered, ppp 0x7fb14e0, ppp->lolayer 0x7333e04
    ## 2011-05-24 19:56:01: stand alone serial1/0 goes to NCP

  4. Negotiate IPCP and other Parameters:

    Negotiate the header compression and IP addresses used for the link, as well as parameters for the other protocols. IPCP is responsible for configuring, enabling, and disabling the IP protocol modules on both ends of the point-to-point link. IPCP uses the same packet exchange mechanism as the Link Control Protocol (LCP).

    ## 2011-05-24 19:56:01: serial1/0, IPCP , fsm open, state : INITIAL -> STARTING
    ## 2011-05-24 19:56:01: serial1/0, fsm_lowerup: layer is up (state=1), f 0x7fb15c4, f->flags 0
    ## 2011-05-24 19:56:01: [PPPSEND]:(serial1/0) ppp_output:(ppp 0x7fb14e0/lolayer 0x7333e04): ppp_output_callback 0x5be6c0, sending len 14:
    ff:3:80:21:1:5:0:a:3:6:98:b3:7a:26:
    ## 2011-05-24 19:56:01: SEND DECODE:(serial1/0) ***[IPCP ConfReq ID=0x5 <ADDR 192.168.1.38>]***
    ## 2011-05-24 19:56:01: serial1/0, IPCP , fsm lowerup, state : STARTING -> REQSENT
    ## 2011-05-24 19:56:01: serial1/0, event 0x6 occurs when LCP is OPENED
    ## 2011-05-24 19:56:01: serial1/0, LCP, fsm input, state : REQSENT -> OPENED

    ppp decap pak:
    2d3b3052: 50 c5 8d 74 ca 96 13 cc 33 cc cc 33 88 8a ff 03 P..t.... 3..3....
    2d3b3062: 80 21 01 08 00 0a 03 06 98 b3 7a 25 .!...... ..z%
    ## 2011-05-24 19:56:01: serial1/0, ppp serial decap process the data pak, proto 0x8021
    ## 2011-05-24 19:56:01: serial1/0, ppp control panel take the pak.
    ## 2011-05-24 19:56:01: [PPPRECV]:(serial1/0) ppp_get_input:(ppp 0x7fb14e0/lolayer 0x7333e04): received len 14:
    ff:3:80:21:1:8:0:a:3:6:98:b3:7a:25:
    ## 2011-05-24 19:56:01: RECV DECODE:(serial1/0) ***[IPCP ConfReq ID=0x8 <ADDR 192.168.1.37>]***
    ## 2011-05-24 19:56:01: serial1/0 recv 0x8021 pak
    ## 2011-05-24 19:56:01: code=2 nakloops=0 max=5
    ## 2011-05-24 19:56:01: [PPPSEND]:(serial1/0) ppp_output:(ppp 0x7fb14e0/lolayer 0x7333e04): ppp_output_callback 0x5be6c0, sending len 14:
    ff:3:80:21:2:8:0:a:3:6:98:b3:7a:25:
    ## 2011-05-24 19:56:01: SEND DECODE:(serial1/0) ***[IPCP ConfAck ID=0x8 <ADDR 192.168.1.37>]***
    ppp decap pak:

    2d3b07e2: 50 c5 8d 74 ca 96 31 cc 33 cc ce 33 88 8a ff 03 P..t..1. 3..3....
    2d3b07f2: 80 21 02 05 00 0a 03 06 98 b3 7a 26 .!...... ..z&
    ## 2011-05-24 19:56:01: serial1/0, ppp serial decap process the data pak, proto 0x8021
    ## 2011-05-24 19:56:01 : serial1/0, ppp control panel take the pak.
    ## 2011-05-24 19:56:01 : [PPPRECV]:(serial1/0) ppp_get_input:(ppp 0x7fb14e0/lolayer 0x7333e04): received len 14:
    ff:3:80:21:2:5:0:a:3:6:98:b3:7a:26:
    ## 2011-05-24 19:56:01 : RECV DECODE:(serial1/0) ***[IPCP ConfAck ID=0x5 <ADDR 192.168.1.38>]***
    ## 2011-05-24 19:56:01 : serial1/0 recv 0x8021 pak

    ## 2011-05-24 19:56:01 : ipcp_up: *** IPCP is up (ppp/f):(7fb14e0/7fb15c4) ***
    ## 2011-05-24 19:56:01 : ipcp_up: *** IP: Local 192.168.1.38, Remote 192.168.1.37 ***
    ## 2011-05-24 19:56:01 : ipcp_up: *** Primary DNS: Local 0.0.0.0, Remote 0.0.0.0 ***
    ## 2011-05-24 19:56:01 : ipcp_up: *** Secondary DNS: Local 0.0.0.0, Remote 0.0.0.0 ***
    ## 2011-05-24 19:56:01 : ipcp_up: *** Primary NBNS: Local 0.0.0.0, Remote 0.0.0.0 ***
    ## 2011-05-24 19:56:01 : ipcp_up: *** Secondary NBNS: Local 0.0.0.0, Remote 0.0.0.0 ***
    ## 2011-05-24 19:56:01 : serial1/0 IPCP is UP
    ## 2011-05-24 19:56:01 : serial1/0, get peer MRU 4470 on protocol UP
    ## 2011-05-24 19:56:01 : serial1/0, add in host route to 192.168.1.37

  5. Ongoing data compression and assignment of links to a multilink, using bandwidth on demand.

    ## 2011-05-24 19:56:01 : serial1/0, ppp serial decap process the data pak, proto 0x21
    ## 2011-05-24 19:56:01 : serial1/0, start to encap ppp data pak for serial port
    ## 2011-05-24 19:56:01 : ppp encap IP packet.
    ppp packet after encap:
    0270aa00: ff 03 00 21 45 00 00 28 26 b0 00 00 40 06 5a 6b ...!E..( &...@.Zk
    0270aa10: 98 b3 7a 26 47 32 9f a9 01 bb 04 5e 4a dd 68 55 ..z&G2.. ...^J.hU
    0270aa20: 84 ae 99 aa 50 18 fd f9 ....P...
    ## 2011-05-24 19:56:02 : serial1/0, start to encap ppp data pak for serial port
    ## 2011-05-24 19:56:02 : ppp encap IP packet.


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