Re: Fwd: Re: How to make my iSeries at home available to outside programmers

[Scott Klement <klemscot@xxxxxxxxxxxx>]

On Wed, 17 Jul 2002 vhamberg@attbi.com wrote:
>
> I've only set up routes on the 400 and gateways in
> various flavors of Windows.

Same thing.  When you say "default gateway" and "default route" you are
using two terms that mean the same thing.   In the GUI interface, Windows
has a way of specifying default gateways (but does not have a way of
specifying other types of routes in the GUI)   So, a "gateway" in the
Windows GUI is the same as "*DFTROUTE" on the 400.

> On the 400 you can specify a
> certain "destination" subnet (net address & mask) that
> will use a certain "next hop" -- as you know. I've never
> seen this in Windows - of course, I've also not needed
> it. Is it there? I just looked at XP - only the gateway
> (next hop) address can be specified - nothing about the
> destination subnet is listed there.
>

>From the command-line (MS-DOS prompt) in Windows, you have a "route"
command which can be used to add/delete routes and also to display
the current routing table.  With this command, you can specify destination
subnets.

I've used it on my Win98 box at home when I had a PPP connection to my
intranet at work, and a separate cable modem to the Internet.   In that
circumstance, I added a route to use the PPP connection only for my
intranet's subnet, so that the default gateway would continue to be my cable
modem for internet...

>
> It appears I did not need that route. It is no longer on
> the 400, and I think someone may have removed it. Or
> would it just have got rolled up into *DFTROUTE
> automagically? I was not sure, and wanted to explicitly
> direct things through the LinkSys. The 400 has an
> address of x.x.x.211, with next hop of x.x.x.214, which
> is the address on the inside of the DSL modem. That gets
> us out the subnet assigned by our ISP.
>

Oh, so the 400 has a public IP, and you added a route to tell it how to
get to the private IPs...  that would work, but it would be redundant if
the same router is used for your *DFTROUTE.

Here's a quick guide to understanding routes (if you already know this
stuff, then I'm sure someone else reading this will find it informative)

    1)  A subnet is a list of IP addresses formed by doing a bitwise
          and of a netmask with an address.   For example, with the
          address 192.168.0.1 and netmask 255.255.255.0, the subnet
          is 192.168.0 and the rest of the address (in this case the 1)
          specifies the actual host within that subnet.

    2)  TCP/IP allows a computer to send packets directly to computers
          in the subnet(s) of the local interface(s).  And that's it.
          You cannot send packets to a computers in any other subnet.

    3)  A route is used to solve that problem.  When you have a route
          you say "I can't send packets to (insert-foreign-subnet-here)
          so, instead send them to (insert-computer-in-local-subnet-here)."

    4)  A default route (or "default gateway") is a catch-all.  It
          basically means "If I try to send packets to a foreign subnet
          that I don't have another route for, then use this route".

    5)  A gateway (sometimes called a "router") is no different, except
          that it can receive packets that are intended for another
          computer, and forward them on according to it's own routes.

So, routing is really quite simple.   You just keep sending the packet
on according to the routes, until finally one machine knows what to do
with it :)