Olaf Kirch: Linux Network Administrator Guide, Second Edition

# nnmaster -lrC

There are many more flags that fine-tune the nn 's behavior. If you are concerned about removing bad articles or assembling article digests, read the nnmaster manual page.

nnmaster relies on a file named GROUPS , which is located in /var/lib/nn . If it does not exist when nnmaster is first run, it is created. For each newsgroup, it contains a line that begins with the group's name, optionally followed by a time stamp and flags. You may edit these flags to enable certain behavior for the group in question, but you may not change the order in which the groups appear. [143] Their order has to agree with that of the entries in the (binary) MASTER file. The flags allowed and their effects are detailed in the nnmaster manual page, too.

Throughout this book we've used the following example that is a little less complex than Groucho Marx University and may be closer to the tasks you will actually encounter.

The Virtual Brewery is a small company that brews, as the name suggests, virtual beer. To manage their business more efficiently, the virtual brewers want to network their computers, which all happen to be PCs running the brightest and shiniest production Linux kernel. Figure A.1 shows the network configuration.

On the same floor, just across the hall, there's the Virtual Winery, which works closely with the brewery. The vintners run an Ethernet of their own. Quite naturally, the two companies want to link their networks once they are operational. As a first step, they want to set up a gateway host that forwards datagrams between the two subnets. Later, they also want to have a UUCP link to the outside world, through which they exchange mail and news. In the long run, they also want to set up PPP connections to connect to offsite locations and to the Internet.

The Virtual Brewery and the Virtual Winery each have a class C subnet of the Brewery's class B network, and gateway to each other via the host vlager , which also supports the UUCP connection. Figure A.2 shows the configuration.

Figure A.1: The Virtual Brewery and Virtual Winery subnets

Figure A.2: The Virtual Brewery Network

The Virtual Brewery grows and opens a branch in another city. The subsidiary runs an Ethernet of its own using the IP network number 172.16.3.0 , which is subnet 3 of the Brewery's class B network. The host vlager acts as the gateway for the Brewery network and will support the PPP link; its peer at the new branch is called vbourbon and has an IP address of 172.16.3.1 . This network is illustrated in Figure A.2.

If you wish to connect two computers together and you don't have an Ethernet network, you will need either a serial null modem cable, or a PLIP parallel cable.

These cables can be bought off the shelf, but are much cheaper and fairly simple to make yourself.

To make a parallel cable to use for PLIP, you will need two 25-pin connectors (called DB-25) and a cable with at least eleven conductors. The cable must not be any longer than 15 meters (50 feet). The cable may or may not have a shield, but if you are building a long cable, it is probably a good idea to have one.

If you look at the connector, you should be able to read tiny numbers at the base of each pin - from 1 for the pin at the top left (if you hold the broader side up) to 25 for the pin at the bottom right. For the null printer cable, you have to connect the following pins of both connectors with each other, as shown in Figure B.1.

All remaining pins remain unconnected. If the cable is shielded, the shield should be connected to the DB-25's metallic shell on just one end.

A serial null modem cable will work for both SLIP and PPP. Again, you will need two DB-25 connectors. This time your cable requires only eight conductors.

You may have seen other NULL modem cable designs, but this one allows you to use hardware flow control - which is far superior to XON/XOFF flow control - or none at all. The conductor configuration is shown in Figure B.2:

Again, if you have a shield, you should connect it to the first pin at one end only.

Figure B.1: Parallel PLIP cable

Figure B.2: Serial NULL-Modem cable

Copyright © 1993 Olaf Kirch Copyright © 2000 Terry Dawson Copyright on O'Reilly printed version © 2000 O'Reilly& Associates

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Permission is granted to copy, print, distribute, and modify the online document under the terms of the GNU Free Documentation License, Version 1.1, or any later version published by the Free Software Foundation; with the Invariant Sections being the Acknowledgments (in the Preface ) and Appendix C, Linux Network Administrator's Guide, Second Edition, Copyright Information. Further acknowledgments can be added outside the Invariant Section. The Front-Cover Text must read:

Linux Network Administrator's Guide

by Olaf Kirch and Terry Dawson

Copyright © 1993 Olaf Kirch

Copyright © 2000 Terry Dawson

Copyright on O'Reilly printed version © 2000 O'Reilly& Associates

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Version 1.1, March 2000

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