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Re: [nv-l] CNAT 2.1 configurations

To: pstroud@bellsouth.net
Subject: Re: [nv-l] CNAT 2.1 configurations
From: Jane Curry <jane.curry@skills-1st.co.uk>
Date: Tue, 22 Apr 2003 21:00:03 +0100
Cc: "Alan E. Hennis" <Hennis_Alan_E@cat.com>, NetView mailing list <nv-l@lists.tivoli.com>, tme10 <tme10@lists.tivoli.com>
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Many thanks, chaps.  It's getting clearer.
So, what's the issue with running the one-armed router on your NetView system (other than making for complex static routing tables)?

Paul Stroud wrote:

We have the one-armed router setup here and it works fine.
Here are the specifics:

Translated range (
maps one-to-one to true range(

Here is the setup

Router A                   Router B
   |                               |

All incoming packets from Router A to the translated range
are sent to CNAT.

All outgoing packets(true address) are sent back to Router A
which then handles the routing of the packet from there.

Here is an example:
Packet G is addressed to and comes into Router A,
it is then routed to CNAT which translates the packet to which is then routed back to Router A which
routes the packet to its destination. The return packet must go
back through CNAT regardless, so the default router for all addresses is the CNAT machine itself. If the
packet needs to be translated, it will be, if not it will be passed
untranslated to Router A which will again route the packet to
its destination.

Remember, the biggest thing about CNAT is the routing. Map
out the path the packet is going to take and make sure that
it is going where it needs to go to be (un)translated.

I'm sure at this point I have just confused the issue, but I'm
just trying to help;-()


On Tuesday 22 April 2003 08:58, Alan E. Hennis wrote:

My understanding of the "one-armed router" is as follows.

In an two interface CNAT configuration you have a box in-line with the
NetView or TEC system. All traffic must flow through the CNAT box to get to
the NetView/TEC box.

NetView/TEC ----------- CNAT BOX ------------ Your Network

In a one-arm router the CNAT box has only one interface (i.e. packets flow
in and out the same interface). Static routes are used to make all your
network traffic flow to the CNAT box and then to the NetView/TEC box

                   CNAT BOX

NetView/TEC -----------+------------ Your Network

In the one-arm router packets flow to the CNAT box and then back out to the
NetView/TEC box.

As far as configuration, I am still trying to make the one-arm router work.

Alan E. Hennis
Caterpillar Inc.
Systems+Process Division

                     Jane Curry

                     04/22/2003 05:03   To: NetView mailing list
<nv-l@lists.tivoli.com> AM                     tme10
<tme10@lists.tivoli.com> cc:

                                          Subject:      [nv-l] CNAT 2.1

Caterpillar: Confidential Green                 Retain Until: 05/22/2003
                                               Retention Category:  G90 -
                                               Information and Reports

The Comprehensive Network Address Translation (CNAT) 2.1 package that
now comes with TEC 3.8 says in the Release Notes that there are 2 new
supported configurations:

* Primary CNAT only, with no redundancy, on a system with one or two
interfaces. A CNAT with a single interface is referred to as a
?one-armed router?
* Primary CNAT installed on a NetView 6.x or newer system. Redundancy is
supported with this configuration, and the CNAT cannot act as a ?one-armed
router? (the CNAT is performing translation for the benefit of NetView

I cannot find any further references in either the Release Notes or the
User's Guide and no entries when searching the IBM Support site.

Does anyone have any further details ojn this "one-armed router" (like
how to configure it) and on using CNAT to perform translation for
NetView only. Why can I not combine the one-armed router with
translating for NetView only?

Many thanks for any input,

Tivoli Certified Consultant & Instructor
Skills 1st Limited, 2 Cedar Chase, Taplow, Bucks, SL6 0EU, UK
Tel: +44 (0)1628 782565
Copyright (c) 2003 Jane Curry <jane.curry@skills-1st.co.uk>.  All rights 

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