LCP Echo Request/Reply "data" field - PPP

This is a discussion on LCP Echo Request/Reply "data" field - PPP ; Hello, What is the right way to reply an LCP Echo Request?. I used to reply this (including in the data field the received Magic Number): [0x0A] / [Id] / [Length] / [Magic Number (local)] / [Received MG + Received ...

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Thread: LCP Echo Request/Reply "data" field

  1. LCP Echo Request/Reply "data" field

    Hello,
    What is the right way to reply an LCP Echo Request?.
    I used to reply this (including in the data field the received Magic
    Number):
    [0x0A] / [Id] / [Length] / [Magic Number (local)] / [Received MG +
    Received Data]
    but I am having problems on some old-discontinued (1999) Intel Routers (it
    seems they don't understand my LCP Echo Replies, so they close the link).
    I have changed my ppp code to reply this:
    [0x0A] / [Id] / [Length] / [Magic Number (local)] / [Received Data]
    and works fine.
    The first method was tested against pppd, cisco, nortel and some other
    vendors and i didn't have any problem. Is it wrong?.

    Many thanks.




  2. Re: LCP Echo Request/Reply "data" field

    "David Rodríguez" writes:
    > I used to reply this (including in the data field the received Magic
    > Number):
    > [0x0A] / [Id] / [Length] / [Magic Number (local)] / [Received MG +
    > Received Data]


    What is "Received MG?" If that's the peer's magic number, then, no,
    that's not right. You just put the data portion there and overwrite
    the peer's magic number.

    > I have changed my ppp code to reply this:
    > [0x0A] / [Id] / [Length] / [Magic Number (local)] / [Received Data]
    > and works fine.
    > The first method was tested against pppd, cisco, nortel and some other
    > vendors and i didn't have any problem. Is it wrong?.


    Yep. Data -> Data.

    --
    James Carlson, IP Systems Group
    Sun Microsystems / 1 Network Drive 71.234W Vox +1 781 442 2084
    MS UBUR02-212 / Burlington MA 01803-2757 42.497N Fax +1 781 442 1677

  3. Re: LCP Echo Request/Reply "data" field

    "James Carlson" escribió en el mensaje
    news:xoavbrofdo9z.fsf@sun.com...
    > "David Rodríguez" writes:
    > What is "Received MG?" If that's the peer's magic number, then, no,
    > that's not right. You just put the data portion there and overwrite
    > the peer's magic number.


    Exactly, that's what I was doing wrong, to include the peer's magic number
    in data portion.
    Thank you very much.

    > > I have changed my ppp code to reply this:
    > > [0x0A] / [Id] / [Length] / [Magic Number (local)] / [Received Data]
    > > and works fine.
    > > The first method was tested against pppd, cisco, nortel and some other
    > > vendors and i didn't have any problem. Is it wrong?.

    >
    > Yep. Data -> Data.


    Then, since the previous wrong lcp echo schema was working for years (and so
    many vendors)...
    I ask myself: the data portion in lcp echo replies is not verified
    habitually, is it?



  4. Re: LCP Echo Request/Reply "data" field

    "David Rodríguez" writes:
    > Then, since the previous wrong lcp echo schema was working for years (and so
    > many vendors)...
    > I ask myself: the data portion in lcp echo replies is not verified
    > habitually, is it?


    Commonly not, no. Many implementations just check that something was
    received, because they use LCP Echo-Request/Response to check link
    liveness.

    (On the Solaris version of pppd, we [optionally] send a couple of LCP
    Echo-Request messages with 256 bytes of data right after opening LCP
    -- containing all possible data byte values. The idea is to make sure
    that connections with a misconfigured ACCM fail quickly rather than
    lingering with strange and hard-to-diagnose errors. If I ever have a
    spare moment, I'll probably integrate that feature into the open
    source version.)

    --
    James Carlson, IP Systems Group
    Sun Microsystems / 1 Network Drive 71.234W Vox +1 781 442 2084
    MS UBUR02-212 / Burlington MA 01803-2757 42.497N Fax +1 781 442 1677

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