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Generate Revenue Through IT Using Business Service Management
Sponsored by HP
Making sure that your business applications are available to their end users is an important part of running your business smoothly. Business operations have evolved to where IT must now broaden its focus to help the company attract, retain and grow customer relationships and increase customer satisfaction. Business service management (BSM) helps lay the foundation by managing services in dynamic support of business requirements. »
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Managing the Modern Network
Sponsored by HP
Networks are more than vehicles to transport e-mail and Web pages. In a global economy where information crosses the globe in an instant, and where Web-based applications power business, it's more important than ever to ensure your network is safe from threats and optimized to deliver the data your business needs. »
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Storage Networking 2, Configuration and Planning
Sponsored by HP
In Part 1, we discussed storage area networks (SANs) and fibre channel. In Part 2, delve into best practices and cover the general concepts you must know before configuring SAN-attached storage. The most critical, sometimes tedious, part of setting up a SAN is configuring each individual disk array. This guide examines configurations for SAN-attached servers and disk arrays, and also includes a look at the future of IP storage.
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Is Your Disaster Recovery Plan Good Enough? Get Disaster Recovery Right
Sponsored by HP
Preparing for a disaster is more often than not part of the storage planning process, and without question it is one of the most difficult task, since it includes local hardware and software, networking equipment, and a test plan to ensure that you can recover from the disaster. Learn how to put your organization on the proper disaster recovery plan, now. »
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Linux Networking: Using Ipchains
Multiple Machines, A Single Connection

William Wong
Monday, July 24, 2000 08:05:03 AM
Linux can route network traffic from one network segment to another. Routing
is normally done on a PC with two or more network adapters. This article
presents a configuration using a pair of Ethernet adapters. More specifically,
the article examines how a Linux computer can link a local network to the
Internet through an Ethernet-attached device like a cable modem or a DSL modem.
The article examines the basic concepts pertaining to routing, network address
translation (NAT), firewalls, and a program called ipchains.
Individual sections address each concept. The last section combines the
basics into a sample configuration for linking a local network to the Internet.
Routing 101
Routing can be done using a number of network protocols but the IP protocol is
the one that is addressed in this article. IP is also the protocol used on the
Internet. The previous articles address configuration of the IP protocol for
network adapters on a Linux computer.
Linux can implement very complex routing using multiple network adapters,
but most configurations utilize a pair of network adapters. These can be any
combination from a pair of Ethernet adapters to an Ethernet adapter and a
modem. This article will concentrate on the former, while the next article will
address the latter.
The routing software, or simply router, listens at a network adapter for
messages, also called packets, addressed to it in the same way as the Apache
web server, httpd, listens for Web-page requests. Many services can use a
single network adapter without a conflict. Other computers on the network
direct messages to the router. The other computers are setup to do this by
setting the IP address of the router in the computer's default router or
gateway setting.
The router takes incoming messages and checks the destination IP address to
determine where to forward the message. It uses routing tables to make this
determination. The message may wind up being sent to another network segment or
it may be forwarded yet again to another computer acting as a router. This
router-to-router handoff is essentially how the Internet works. A
router-to-router handoff is called a hop. Messages going in the reverse
direction are handled in the same fashion.
The router assumes the network adapter handles the low level transmission of
messages. For modem links, like those covered in the next article, often
utilize the Point-to-Point Protocol (PPP). Some DSL and cable modems utilize
PPP over Ethernet (PPPoE). For this support, check in the next article. This
article assumes that DSL and cable modems are connected to an Ethernet adapter.
The Linux route program is used to configure and display the routing tables.
The routing support is built into Linux. The basic syntax and semantics for the
route program are covered later.
Next: Network Address Translation 101 »