Exporting a display over a dialup bridge?

Discussion in 'Linux Networking' started by Ben, Dec 16, 2003.

  1. Ben

    Ben Guest

    I hope the diagram isn't too screwed up.

    A B C
    ---- ---- ----
    | |------------| | | |
    | | | |---------------| |
    ---- ---- ----

    I want to export a display to A from C via B. B has 2 interfaces
    active, the normal LAN connection and a PPP dialup to C. Machine C
    does not have SSH so I can't use port forwarding. I've tried various
    combinations of exporting the display and building routes, but nothing
    seems to work. Is this even possible? It's bugging the poop out of me.

    Any ideas are appreciated.
    Ben, Dec 16, 2003
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  2. Ben

    jack Guest

    It is possible, and that is relatively easy.

    First off, is the setup You describe above really correct? - Pardon me,
    but it is a rather unusual setup.

    Then, You can easily forward any traffic from C to A via B, and I may
    assume that You have the basic knowledge on how to do that.

    Two things to add are that (1) remember that 10.* is a private IP range,
    so eventually B _must_ masquerade the traffic from C, and (2), A must
    allow remote connections from the outside ("xhost +").

    There should be absolutely no problem - You will get it to work.

    After that, go use ssh tunneling and a proper rule for xhost. - But for
    testing, this is really straightforward and should work.

    If You yet encounter problems, see whether Your X-Server (A) listens
    at a corresponding C socket to X11 connections (6000; 5000).

    Should work, sorry. If this doesn't help, send more details like fw logs
    and the like.

    Cheers, Jack.
    jack, Dec 16, 2003
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  3. Ben

    jack Guest

    Sorry - or, "pardon me", - I misread A for C (plus a few otehr details).
    It's not unusual, and even if it was, my previous answer stays intact.

    Sorry for the confusion, Jack.
    jack, Dec 16, 2003
  4. Ben

    Leon. Guest

    No, I got it. B dials C, and hopes to put C on the LAN.

    Your mistake has been to put the 10.93.4.* addresses on the PPP link.
    Why did you do this ? I guess you saw some diagram where it was done like
    But in those diagrams, C belongs to a different network to A.

    When you want C to be part of A, each end PPP link gets the Ip addresss of
    B and C on the 143.209.219. network. PPP is also told to 'proxy-arp' which
    means that B will tell A that the MAC address for C is B's mac address. A
    then sends (at the ethernet level) packets for C to B, and when B gets them
    B recognises them as packets for C (despite the "hoax" destination mac
    address) and send them on to C. Packets returning from C to A have no

    Or if you like you can leave you ip address strategy alone, and add the

    On A, add a route to C via B (B's 142.209.219.* address)

    On C , add a route to the network via the PPP
    interface (or B=

    B will have correct routing.

    However whatever the ip address scheme and routing, A . B and C need their
    firewalls and networking properly configured.

    A and C needs to have firewalls checked.

    B needs to have its firewall checked, and also it needs to have 'ip
    forwarding' turned on, in the config screen of the distribution it may be a
    check box 'act as router' or 'act as gateway' , probably on the screen where
    you give it an ip address netmask and gateway address.
    Leon., Dec 17, 2003
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