PPP Question on Receiving an LCP Config - PPP

This is a discussion on PPP Question on Receiving an LCP Config - PPP ; Hello, I'm a newbie to this group, so please bear with me... I'm debugging a wireless connection where I see the PPP link and network layers, being renegoiated every 30 seconds or so. I never get an LCP Terminate. The ...

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Thread: PPP Question on Receiving an LCP Config

  1. PPP Question on Receiving an LCP Config

    Hello,

    I'm a newbie to this group, so please bear with me...

    I'm debugging a wireless connection where I see the PPP link and network
    layers, being renegoiated every 30 seconds or so. I never get an LCP
    Terminate. The connection starts up normally, link and network layers come
    up, I pass some tcp traffic and then out of the blue the DCE sends me an LCP
    Config request. My mobile then responds with LCP Configs and then IPCP is
    negoiated again.

    My question is, can I assume that the receipt of an LCP Config during an
    established connection breaks the link and network layer and forces a
    reconnect? Or is the LCP terminate the only way to break the connection? If
    the PDSN wanted the connection torn down, wouldn't an LCP Terminate be sent
    out?

    Sorry in advance if this is too basic a question.

    Thanks,
    RDT



  2. Re: PPP Question on Receiving an LCP Config

    "janet chmura" writes:
    > I'm debugging a wireless connection where I see the PPP link and network
    > layers, being renegoiated every 30 seconds or so. I never get an LCP
    > Terminate. The connection starts up normally, link and network layers come
    > up, I pass some tcp traffic and then out of the blue the DCE sends me an LCP
    > Config request. My mobile then responds with LCP Configs and then IPCP is
    > negoiated again.


    There are many things that could cause this, including subtle bugs on
    either side or even hardware problems. It would help a *lot* if you'd
    include debug logs in your next posting so that someone can analyze
    the problem more completely. (Text descriptions of a problem are just
    never a good substitute for actual log messages.)

    > My question is, can I assume that the receipt of an LCP Config during an
    > established connection breaks the link and network layer and forces a
    > reconnect? Or is the LCP terminate the only way to break the
    > connection?


    Receipt of LCP Configure-Request forces the LCP state machine from
    Opened to either Ack-Sent or or Req-Sent state (the former if all of
    the requested options are fine and LCP Configure-Ack was sent in
    reply, the latter otherwise), and causes event 'tld'. That event
    causes the network layers to be torn down (transitioning from Opened
    to Starting), and effectively pushes the overall PPP state machine
    back into "Establish" phase. This means that you must go through LCP
    negotiation again, through authentication (if any is configured), and
    through NCP negotiation.

    However, how the PPP state machine relates to the software outside of
    PPP (the network and physical layers) is really an internal
    implementation issue, and isn't (and can't) be specified by a standard
    of this sort, since it's a matter that's not visible outside of the
    system.

    In other words, an implementation would be free to leave the IP
    interface up while doing PPP renegotiation, on the optimistic
    assumption that the renegotiation would quickly complete and come out
    with exactly the same parameters (addresses, MTU/MRU) as the last
    time. If it didn't, then it might have to tear down the link and
    bring it back up, depending (again) on the APIs provided to networking
    applications -- something also intentionally not specified as a part
    of IETF standards.

    I'd expect, though, that most implementations would take the simple
    route -- tearing down the IP interface when LCP Configure-Request is
    seen, and bringing it back up when IPCP transitions to Opened state.

    > If
    > the PDSN wanted the connection torn down, wouldn't an LCP Terminate be sent
    > out?


    Yes. Or you'd just lose the physical layer (i.e., see carrier drop).
    (Sending LCP Terminate and waiting for the response is a polite way to
    tear down the link, as the message has room for a text message that
    can be used to tell a human why the link was terminated. There's no
    *requirement*, however, that anyone be this polite.)

    --
    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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