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Re: (ASCEND) second (Pipeline) router on a LAN

On Tue, 17 Mar 1998, Billy Matthews wrote:

> I have a small LAN with an Ascend ISDN Pipeline 50 router connected to
> an ISP, and am adding a second Pipeline router to connect to another
> office.  

It all depends, in part, as to whether you are using NAT or not.  This is
one of those rare cases where having NAT actually increases what you can
do with yourself.

Here's how I understand it:

<internet> -ISDN- P50 -ether- LAN -ether- P50 -ISDN- P50 -ether- LAN2

How you do this will be determined by how you have your IP's laid out.

Do you have NAT from your upstream provider, or regular IP addresses?  If
you have regular IP's, you will have to get one for the P50 on the first
LAN, then (unless your upstream wants to give you another stack of IP's
for the other office) set up NAT on the P50 on the LAN-2, so that you have
that network using only 1 global IP.

If you have NAT, then you presumably are already using a subnet such as
10.0.0.0/8 or 192.168.0.0/16.  You must split this net in half and give
half of your IP's to the "far" network.  For example,

<internet> -P50- LAN(192.168.0.0/17) -P50- -P50- LAN2(192.168.128.0/17)

Now you have to assign the systems on the first LAN IP's in 192.168.0.0 to
192.168.127.255 and give them netmasks of 255.255.128.0.  The systems on
the second LAN will now have IP's between 192.168.128.0 and
192.168.255.255.  Now you must simply assign a static route on the P50's
connecting the two LAN's to route between these two halves of your NAT
assigned IP's.  The farthest P50 in the chain will then set its default
route to the P50 on the other end of its ISDN link, and that P50 will
(like all the other hosts on that network) set its default route being the
P50 connected to the internet.

This is assuming that the second LAN only connects to the Internet by way
of the first LAN.  You MIGHT have a situation such as the follows:

    |------- INTERNET -------------|
   P50                            P50
      \                          /
      LAN1 - P50 -ISDN- P50 - LAN2

In this case, if you are using NAT, you can set up your IP's as before.
Give one LAN 192.168.0.0/17 and the other LAN 192.168.128.0/17, and let
the P50's route between them, and the default routes go to the P50's
connected to the Internet.

Note that these solutions may require that that you renumber one or both
of these networks.  There's not much that can be done about that, 

If your LAN's are both NOT using NAT, then you will of course use whatever
IP's they have already, rather than the ones used in a typical NAT
install.  The P50's can route between them statically, and traffic between
the LAN's will go over the one link, while traffic to/from the Internet in
each case will go over the normal Internet links.  This is kind of a nice
setup because you get redundancy - any one of the links can go down
without destroying the ability to connect to any other site.

> connects outbound to the ISP.  Static routing on each client is probably
> a bit difficult, since we run both Win 95 and NT Wks clients.  I am not

Shouldn't make any difference.  The systems on the ethernet should never
have to care what they use to connect to the rest of the world.  That is
what routers do.

> sure how to setup routing on the Pipeline units, and RIP is really not
> attractive, since it seems to connect to the other office every 30
> seconds.

You don't need RIP for this.  You can setup a call filter to block the RIP
broadcasts from bringing up the connection, but there's no need for
dynamic routing here, your setup is not complicated enough for it.

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