[H-GEN] routing, subnets, and TCP/IP

[Martin Pool]

(Note reply-to: being general at humbug.org.au vs Martin Pool <martinp at mincom.com>)

Doug Young wrote:

> OK ..... so I guess you mean the LAN gateway box is one "peer" and the ISP
> or equivalent is the other "peer" ??

That's right: an ethernet connects up any number of machines, whereas a
modem/phoneline connects one machine to another.  This is why we call it
a "point-to-point" (PtP) connection.

> > # /sbin/ifconfig ppp0
> > ppp0      Link encap:Point-to-Point Protocol
> >           inet addr:203.109.211.201  P-t-P:203.109.211.190
> >
> > Your end of the PPP link is associated with the first address; the other
> end
> > is assoicated with the other address.  In order for you to be able to
> reach
> > that machine, you must have a route to it:
> 
> I'm trying to figure what you mean exactly ... I assume "Your end of the PPP
> link" is the ppp0 on the LAN gateway box, and "the other address" is the
> eth0 on the same box ??

Your end of the link is indeed the ppp0 device on your machine.  The
other address is the machine your modem is talking to, which is
typically a terminal server at your ISP.  


    [W95] (eth) ------- (eth0) [Linux] (ppp0) ----- (ppp) Annex (eth0)
-------
                                      .211.201    .211.190              

The "routing" and "IP forwarding" commands people discussed before tell
your Linux box that it should intelligently copy packets between the two
interfaces so that the Windows box can see the internet.

> The rest I'll try to absorb gradually by sketching it out on paper  .....
> however I don't need to mess with firewalls or DHCP immediately if they
> aren't strictly essential to basic functionality so is there any other
> reason I need to be concerned with that stuff ??

You probably will want a firewall for some kind of protection but you
can build that up gradually starting from here.  Even if your machine
isn't providing any protection it's filling a similar role to a firewall
and some of the documentation will be relevant.

-- 
 /\\\  Mincom | Martin Pool          | martinp at mincom.com
// \\\        | Software Engineer    | Phone: +61 7 3303-3333
\\ ///        | Mincom Ltd.          | 
 \///         | Teneriffe, Brisbane  | Speaking for myself only

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