15 Aug 96 , Dave Freeman did fondle the keyboard and wrote to me!:
 Yowser & greets Dave!,

 RVR>> I belong to the "other" group :)

 DF> Then you're in the wrong group.  

Not necessarily :)

 DF> You have a local area network using ethernet interfaces and using
 DF> TCP/IP networking.  Each machine on that network must have it's own
 DF> unique IP address in order for TCP to work properly.  TCP uses those IP
 DF> addresses to route data around and see to it that it ends up in the
 DF> right place.

 DF> You have a wide area network (connection to the internet) using a PPP
 DF> interface and using TCP/IP networking.  Once again, each machine on
 DF> that wide area network must have it's own unique IP address so that
 DF> data ends up where it's supposed to end up.

Ok, that's true in the form of subnets - but why can't the IP for the LAN
be the same as the WAN.

 DF> Now the key point, each of these networks is separate.  If a single
 DF> machine is going to exist in both of these networks then it is going to
 DF> have to have relevant IP address information for each network.

But there is only one network, this is what I have stated in the past - my
LAN is the WAN network.

 DF> If it only has an IP address for the WAN, how is the LAN supposed to
 DF> know how to send it traffic?  If it only has an IP address for the LAN,
 DF> how is the WAN supposed to route traffic to it?

Ok, confusion reigns, I still can't see why if I have 203.17.118.51 and
203.17.118.52 why I can't do an ftp from .52 to .51 and have it work. It
appears to do so here already. Both machines know the other exist.

 DF> This is why an IP address really refers to the INTERFACE rather than
 DF> the computer.  In the above case, one machine is going to have to have
 DF> two IP addresses, one that relates to it's existance in the LAN (an IP
 DF> address for it's ethernet interface) and one that relates to it's
 DF> existance in the WAN (an IP address for it's PPP interface).

I think I understand what you mean, but looking from my *.51, then the ppp
interface is actually *.2 which is the machine at the other end. So you
could actually say my ppp interface is *.2 and my ethernet is *.51

 DF> So, the final part is that it's the routing statements on the machine
 DF> that has both interfaces that is important in getting all the machines
 DF> on your LAN able to use the WAN connection.  This single machine has to
 DF> be able to understand how to take traffic moving over your LAN that
 DF> requires data from a machine not on your LAN and move it over to the
 DF> WAN so that it gets where it has to.  It then has to be able to do the
 DF> reverse, take traffic from the WAN and route it back to the right
 DF> machine on the LAN.

Well I figure the gateway statements had covered this aspect of the routing.

 DF> Wrong.  If you only had a PPP link to your ISP and nothing else then
 DF> you'd only need one IP address, the one for your PPP connection.  If
 DF> you add in an ethernet connection on that same computer then you'll
 DF> also need a second IP address that refers to that other network that
 DF> also happens to be running on that one machine.

But it's not an "other network", I see it as basically an
extension of the 203.17.118.* network.

 DF> The address that is allocated by your IP will certainly work for any
 DF> protocols that are running over the connection between you and your ISP
 DF> but that same IP address will not be suitable for using on your local
 DF> area network as, basically, your LAN won't know how to deal with it.

This is where I am confused, understanding why the LAN cannot know the
whereabouts of the first IP address. I am totally ignorant here because my
LAN does seem to know where the first IP is, all pings etc go to the
applicable machine.

 DF> I've yet to see an ISP that doesn't run multiple machines on a LAN of
 DF> some sort.  When these machines are setup they only have one IP address
 DF> because the only network connection is the ethernet interface. If, on

No, each of his machines have a different IP address.

 DF> the other hand, you look at the terminal server (be it a computer with
 DF> multi-serial cards or a dedicated box like a Cisco or some such) you'll
 DF> find that it has quite a few IP addresses associated with it.  In
 DF> effect, it will have an IP address associated with each serial line
 DF> it's dealing with (which is the IP address that you will be assigned
 DF> when you connect to it), plus an IP address associated with it's
 DF> existance in relation to the serial ports plus another one associated
 DF> with it's existance on a LAN (ethernet) and perhaps even another IP
 DF> address depending on how that box connects to the internet itself (if
 DF> it has built-in ISDN support for example).

This is correct, the server does support multiple IP's, in fact it supports
every IP address between 203.17.118.1 to 203.17.118.255 in one way or
another whether it be a LAN, ppp, etc etc

 DF> I can't think of an easy way for you to test this as it requires a fair
 DF> degree of knowlege of the IPS's layout to start delving into his IP
 DF> addresses but if you talk to your local friendly ISP about it - and if
 DF> they really are that friendly about it - they might be willing to show
 DF> you over their setup and you'll see this sort of thing in action.

Well my entire setup and address's comes from my ISP telling me how to set
it up. My ISP and I are friends (yeah ok, so I do have one or two friends
;-) ), I have been over there on numerous occasions. I have even assisted
resetting some of his machines and am quite familar as to how his system
operates - well physically anyway, eventhough all the tcp stuff may be a
little beyond my understanding.

There is basically one main server, this is because it operates under
Debian Linux and not under Win NT (Win NT ISP's seems to need a number of
machines to play server...). Certain functions are handled by one of the
other few ethernetted machines, each of these have their own IP address
(much the same as my machines do). In reality, none of the other machines
are required to actually run the ISP, but certain file servers etc are
routed from them. Each of these machines have an IP address, one is
actually an entirely different site which I believe is just routed via my
ISP. His machines are setup like mine, the only problem I think I will have
is routing statements across the LAN network of the ISP. This is where your
understanding and explanations come to bear - if I was a separate network,
then it would be as you describe and handled at his end. Since I am not a
separate network, I envisage I will have trouble running across my LAN, up
the ppp link and then down another ppp link to another same network
addressed machine. I figure an immense routing table will fix this :) Then
again, I will not really require access to those machines anyway as there's
nothing for me on them.

Anyway, I've yet to receive my updated sanaII device, so I am stuck with
thinking about it 'til then. Once it arrives I can go through the actual
attempts :)

Cheers,       __
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            / \*icta*...

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