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A little speculation about PPP

johnifanx98johnifanx98 Member Posts: 329
in CCNA & CCENT
I'm thinking of what questions could be asked regarding PPP.

PPP protocol stack has

=====
NCP
LCP
HDLC
=====

HDLC: non-proprietary HDLC. Not much interesting.
LCP: authentication modes?
NCP: looks like important, but barely see anything detailed mentioned about this sublayer in CCNA preparing material.

All in all, what tricky questions would be asked about PPP?
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    drkatdrkat Banned Posts: 703
    PPP and HDLC are different things. PPP is an open standard where as HDLC is cisco proprietary.

    PPP has two underlying layers your LCP/NCP - Link Control and Network Control - your LCP sets up the link handling setup/teardown/keep alive etc and your NCP is used for specific network protocols running over PPP (layer 3 stuff, such as IPX/Netbios/IP etc etc)

    CHAP/PAP are your authentication methods available over PPP

    I dont recall being asked too many of these questions but... you want to familiarize yourself with LCP/NCP and PAP/CHAP attributes - they wont ask you anything CRAZY just the basics.

    They may ask you about if a PPP interface can be looped or not..

    Frame does not respond to a loopback - the interface will actually go down/down if it is in "loopback" however if you're the tech first looking at you'd have no way of knowing this other than by researching or being able to get into the circuit and look for loops.
    PPP goes up/up
    HDLC shows up/up (looped)
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    mikeybikesmikeybikes Member Posts: 86 ■■□□□□□□□□
    drkat wrote: »
    PPP and HDLC are different things. PPP is an open standard where as HDLC is cisco proprietary.

    I think HDLC is an ISO standard.
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    drkatdrkat Banned Posts: 703
    excuse me.. cisco's implementation of HDLC is proprietary and does not work with other vendors such as ADTRAN
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    darkerzdarkerz Member Posts: 431 ■■■■□□□□□□
    HDLC has always been a cisco-tastic proprietary protocol.

    PPP is across the board (Cisco, Juniper, Adtran, Samsung).
    :twisted:
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    Michael2Michael2 Member Posts: 305 ■■■□□□□□□□
    According to the ICND1 Certification Guide by Odom, there is a non-proprietary version of HDLC. I suppose it was developed because HDLC is so fast. However, the non-proprietary version does not include the protocol type field present in Cisco's version.
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    johnifanx98johnifanx98 Member Posts: 329
    Michael2 wrote: »
    According to the ICND1 Certification Guide by Odom, there is a non-proprietary version of HDLC. I suppose it was developed because HDLC is so fast. However, the non-proprietary version does not include the protocol type field present in Cisco's version.

    When incompatible routers are connected, they have to use a certain HDLC as underlying protocol if using PPP. And this HDLC should be the non-proprietary one.
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    johnifanx98johnifanx98 Member Posts: 329
    drkat wrote: »
    PPP and HDLC are different things. PPP is an open standard where as HDLC is cisco proprietary.

    PPP has two underlying layers your LCP/NCP - Link Control and Network Control - your LCP sets up the link handling setup/teardown/keep alive etc and your NCP is used for specific network protocols running over PPP (layer 3 stuff, such as IPX/Netbios/IP etc etc)

    CHAP/PAP are your authentication methods available over PPP

    I dont recall being asked too many of these questions but... you want to familiarize yourself with LCP/NCP and PAP/CHAP attributes - they wont ask you anything CRAZY just the basics.

    They may ask you about if a PPP interface can be looped or not..

    Frame does not respond to a loopback - the interface will actually go down/down if it is in "loopback" however if you're the tech first looking at you'd have no way of knowing this other than by researching or being able to get into the circuit and look for loops.
    PPP goes up/up
    HDLC shows up/up (looped)

    Per my reading, loopback is mainly used to verify the IP module functionality. But, what is the chance of IP module failure?
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    drkatdrkat Banned Posts: 703
    PPP/Frame/HDLC will be used on a WAN link most commonly - loopback testing is a type of testing done at the carrier or CPE end using a loopback plug or software loop - Not the same thing as a loopback interface. Sorry for the confusion.
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    johnifanx98johnifanx98 Member Posts: 329
    drkat wrote: »
    PPP/Frame/HDLC will be used on a WAN link most commonly - loopback testing is a type of testing done at the carrier or CPE end using a loopback plug or software loop - Not the same thing as a loopback interface. Sorry for the confusion.

    If frame does not respond to the loopback, then no serial interface can be tested in this way, including HDLC/PPP/FR?

    I remember the other day one guy asked in the forum how to make T1 loopback plug. I think that's for HDLC?
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    drkatdrkat Banned Posts: 703
    It comes down to encapsulation of the interface whether it responds to loopback or not. Frame relay does not respond to loopbacks. HDLC/PPP do however
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    IllumanatiIllumanati Banned Posts: 211 ■□□□□□□□□□
    johnifanx98 wrote: »
    I'm thinking of what questions could be asked regarding PPP.

    PPP protocol stack has

    =====
    NCP
    LCP
    HDLC
    =====

    HDLC: non-proprietary HDLC. Not much interesting.
    LCP: authentication modes?
    NCP: looks like important, but barely see anything detailed mentioned about this sublayer in CCNA preparing material.

    All in all, what tricky questions would be asked about PPP?

    Thank you for asking! The timing was good for me! I'm in Cisco IV now and we just went over this yesterday!!
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    johnifanx98johnifanx98 Member Posts: 329
    Illumanati wrote: »
    Thank you for asking! The timing was good for me! I'm in Cisco IV now and we just went over this yesterday!!

    Would you share with us what you've gone over?
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    IllumanatiIllumanati Banned Posts: 211 ■□□□□□□□□□
    johnifanx98 wrote: »
    Would you share with us what you've gone over?

    Thank you (for enabling my accountability.) I sure will (Get back with you) and sorry for the delay.
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