Re: PPP-layer Echo

From: Barney Wolff (barney_at_databus.com)
Date: 04/28/05

  • Next message: John-Mark Gurney: "Re: sparc64/80410: netgraph is causing crash with mpd on sparc64" 
    Date: Wed, 27 Apr 2005 20:35:33 -0400
To: cjclark@alum.mit.edu

    On Wed, Apr 27, 2005 at 04:41:52PM -0700, Crist J. Clark wrote:
    >
    > However, I'm seeing some weirdness, and I wonder if any PPP
    > gurus can comment. My end sends a ping (a HDLC dump),
    >
    > ff 03 c0 21 09 01 00 10 6d a8 39 0d 59 4e 4f 54 00 00 00 01 52 b6
    > ^^^^^ ^^^^^ ^^ ^^ ^^^^^ ^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^
    > PPP LCP Id Len. Magic No. Data FCS
    > Echo-
    > Request
    >
    > And receives this,
    >
    > ff 03 c0 21 0a 01 00 14 e8 67 ea ac 6d a8 39 0d 59 4e 4f 54 00 00 00 01 29 35
    > ^^^^^ ^^^^^ ^^ ^^ ^^^^^ ^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^
    > PPP LCP Id Len. Magic No. Data FCS
    > Echo-
    > Reply
    >
    > Which looks a bit strange to me. My end is rejecting those echoes
    > as bogus because the data we send does not match the data we get back.
    > What looks like is happening is that the other end of the PPP
    > is taking the Magic Number field from the echo request and copying
    > it into the data field. That also explains why the response is 4 bytes
    > longer than the request.
    >
    > I'm no PPP expert, but this is looking pretty fishy. Is the other
    > end totally broken? However, RFC1661 isn't totally explicit about
    > how the data field needs to be handled,
    >
    > Data
    >
    > The Data field is zero or more octets, and contains uninterpreted
    > data for use by the sender. The data may consist of any binary
    > value. The end of the field is indicated by the Length.
    >
    > But it seems wrong to modify the data field.

    It is wrong. Is the other end OS/2 or something derived from it? I
    recall, from a decade ago, that this was about what some version of
    OS/2 did wrong. 

    -- 
Barney Wolff         http://www.databus.com/bwresume.pdf
I never met a computer I didn't like.
_______________________________________________
freebsd-net@freebsd.org mailing list
http://lists.freebsd.org/mailman/listinfo/freebsd-net
To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org"
  • Next message: John-Mark Gurney: "Re: sparc64/80410: netgraph is causing crash with mpd on sparc64"