Clarification regarding pppd's demand option - PPP

This is a discussion on Clarification regarding pppd's demand option - PPP ; The man page says: demand - Initiate the link only on demand, i.e. when data traffic is present. With this option, the remote IP address must be specified by the user on the command line or in an options file. ...

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Thread: Clarification regarding pppd's demand option

  1. Clarification regarding pppd's demand option

    The man page says:

    demand - Initiate the link only on demand, i.e. when data
    traffic is present. With this option, the remote IP address
    must be specified by the user on the command line or
    in an options file. ...

    But isn't it really *a* remote IP address, not *the* remote IP address?
    Any IP address that isn't on the local subnet will suffice, won't it?
    If I set up the remote IP address to be x.y.z.q and someone pings
    x.y.z.m (with a suitable subnet mask), won't the connection be
    activated?


  2. Re: Clarification regarding pppd's demand option

    "Chris Nelson" writes:

    > The man page says:
    >
    > demand - Initiate the link only on demand, i.e. when data
    > traffic is present. With this option, the remote IP address
    > must be specified by the user on the command line or
    > in an options file. ...
    >
    > But isn't it really *a* remote IP address, not *the* remote IP address?
    > Any IP address that isn't on the local subnet will suffice, won't it?
    > If I set up the remote IP address to be x.y.z.q and someone pings
    > x.y.z.m (with a suitable subnet mask), won't the connection be
    > activated?


    If you don't specify _the_ remote address, then when the connection
    does activate, you'll be faced with negotiating a connection to some
    peer that's different from the one you originally intended.

    If that's ok in your situation (it might be, but it might not be),
    then that's fine.

    --
    James Carlson, KISS Network
    Sun Microsystems / 1 Network Drive 71.232W Vox +1 781 442 2084
    MS UBUR02-212 / Burlington MA 01803-2757 42.496N Fax +1 781 442 1677

  3. Re: Clarification regarding pppd's demand option

    Hello,

    James Carlson a écrit :
    > "Chris Nelson" writes:
    >
    >>The man page says:
    >>
    >> demand - Initiate the link only on demand, i.e. when data
    >> traffic is present. With this option, the remote IP address
    >> must be specified by the user on the command line or
    >> in an options file. ...
    >>
    >>But isn't it really *a* remote IP address, not *the* remote IP address?
    >> Any IP address that isn't on the local subnet will suffice, won't it?

    [...]
    > If you don't specify _the_ remote address, then when the connection
    > does activate, you'll be faced with negotiating a connection to some
    > peer that's different from the one you originally intended.
    >
    > If that's ok in your situation (it might be, but it might not be),
    > then that's fine.


    Hmm, what happens when the IP address sent by the peer in IPCP ConfReq
    does not match pppd's idea of the remote address ? Does pppd acknowledge
    the peer's address request anyway ?

  4. Re: Clarification regarding pppd's demand option

    Pascal Hambourg writes:
    > Hmm, what happens when the IP address sent by the peer in IPCP ConfReq
    > does not match pppd's idea of the remote address ? Does pppd
    > acknowledge the peer's address request anyway ?


    It depends on pppd's configuration. By default, pppd will send back
    IPCP Configure-Nak and try to tell the peer to use the configured
    address. If the peer refuses to change, pppd will start rejecting the
    IPCP Address option and the link will eventually fall apart.

    If you include the "ipcp-accept-remote" option, pppd will simply send
    IPCP Configure-Ack for that address, and will change the interface to
    suit. This, again, may or may not be compatible with what you're
    trying to do.

    (It might be ok for a link to an ISP where none of your configuration,
    such as DNS server addresses, references that remote address. It
    might not be ok if this is some individual remote node with which you
    need to communicate.)

    --
    James Carlson, KISS Network
    Sun Microsystems / 1 Network Drive 71.232W Vox +1 781 442 2084
    MS UBUR02-212 / Burlington MA 01803-2757 42.496N Fax +1 781 442 1677

  5. Re: Clarification regarding pppd's demand option

    James Carlson wrote:
    > "Chris Nelson" writes:
    >
    > > The man page says:
    > >
    > > demand - Initiate the link only on demand, i.e. when data
    > > traffic is present. With this option, the remote IP address
    > > must be specified by the user on the command line or
    > > in an options file. ...
    > >
    > > But isn't it really *a* remote IP address, not *the* remote IP address?
    > > Any IP address that isn't on the local subnet will suffice, won't it?
    > > If I set up the remote IP address to be x.y.z.q and someone pings
    > > x.y.z.m (with a suitable subnet mask), won't the connection be
    > > activated?

    >
    > If you don't specify _the_ remote address, then when the connection
    > does activate, you'll be faced with negotiating a connection to some
    > peer that's different from the one you originally intended.
    >
    > If that's ok in your situation (it might be, but it might not be),
    > then that's fine.


    Thanks. What I ended up doing was taking the local IP address, setting
    the most significant bit and using that as the remote IP address with
    ipcp-allow-remote so when I ping anything off my subnet, the connection
    is made. Perfect!


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