Re: tlug: Q: Mini-LAN with PPP

["Stephen J. Turnbull" <turnbull@example.com>]

>>>>> "ASH" == Andrew S Howell <andy@example.com> writes:

>>>>> "Manuel" == Manuel Chakravarty <chak@example.com> writes:

    Manuel> Hi!  Yesterday I played a bit with PPP and tried to set up
    Manuel> a kind of mini-LAN between two Linux machine (neither of

I assume you mean using the serial interface with a null-model cable?

If you are doing this with Ethernet cards, there WILL be a lot of
confusion about what interface is wanted.

    Manuel> which is connected to an Ethernet or so).  Setting up the
    Manuel> ppp connection itself was no problem (after reading the
    Manuel> PPP-HOWTO), but I had problems with the routing.  In other
    Manuel> words, I could ping each of the machines from the other
    Manuel> one, but I couldn't use any other IP service, such as

ping _can_ be implemented as a TCP service, but I believe the standard 
Linux one uses ICMP.  So it's different from the ones you're talking
about.  That may be important, although I can't see why.

    Manuel> `rlogin', `telnet' etc. (I got the error message `network
    Manuel> not reachable').  I tried setting the defaultroute on each
    Manuel> machine to the respectively other machine and I had a look
    Manuel> at the `route' man-page, but I couldn't figure out how to
    Manuel> do it properly.

    ASH> The "network not reachable" is saying that there isn't an
    ASH> interface over which to route packets to your destination.

    ASH> To set a default route do:

    ASH> 	route add default gw ppp-ip-addres

PPP should be doing that automatically.  (On second thought, that
depends on the PPP package you're using.  Debian 1.3 certainly does,
though.)  Furthermore, as far as I know `ping' gets its routing
information from the same place as any other IP program.  Finally, as
long as there is a host-to-host route in place, a two-host LAN using
PPP should not need any network routing information other than that
provided automatically by PPP.

I would modify that to 

	       route add -host REMOTE-IP dev INTERFACE
               route add default gw REMOTE-IP

where things in caps are variables.  INTERFACE should be `ppp0'.  It
probably doesn't need to be specified.

This needs to be done on both machines.  If you only do it on one, the 
other will definitely give you "unreachable" errors.

    ASH> If you could send the results of:

    ASH> 	ifconfig -a

    ASH> 	netstat -rn

Yes, please do.

    ASH> from both machines, we'll have a better idea of what it going
    ASH> on.

    Manuel> Did anybody sucessfully use PPP in this way?  If so, how
    Manuel> did you set up the routing?  (I used two IP-addresses from
    Manuel> the range designated for such non-Internet-connected
    Manuel> LANs.)

I do this by phone, with several configurations.

HTH

Steve

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