Today, almost every IT application requires the ability to exchange large quantities of information. High-bandwidth links provide the networking infrastructure to enable data transfer for business and spare-time worldwide. Fast Ethernet LANs provide a transfer rate up to 10 gigabits per second (Gbps). To illustrate this speed, transferring the 700MB contents of a CD-ROM would take approximately half a second.
Linux on System z, the system of choice for medium- to large-scale business applications, supports all standard network interfaces and protocols and offers several powerful features unique to Linux on a mainframe.
PCs usually natively run a single instance of an operating system, controlling the whole computer system. In contrast, IBM System z supports the important concept of virtualization. All operating systems, including Linux, execute in a virtual environment. There may be (and normally are) instances of several different operating systems running simultaneously. To learn more, refer to Linux on the Mainframe (John Eilert et al., Prentice Hall, 2003, ISBN 01310141532) and IBM’s Redbooks (www.redbooks.ibm.com/).
The mainframe is divided into Logical Partitions (LPARs). Each LPAR can either directly execute an operating system, such as the Linux kernel (see Figure 1), or a number of operating system images as “guests” of z/VM. VM is the second way to create a virtual environment executing Linux. A network connection between virtualized Linux systems may itself be virtual. In this case, the communicating parties behave as if they were sending and receiving data via a real network, but the data transfer is much faster and actually performed by moving data in the mainframe’s main memory.
This article presents a short overview of the layered structures of today’s network architectures as well as the networking features provided by the IBM System z mainframe and how they’re used under Linux. Figure 2 summarizes the networking features mentioned in this article that recent Linux distributions support.
Networking Infrastructure Basics
The networking infrastructure is described in two major “blueprints” that are the basic framework for many communication protocols:
• The Open Systems Interconnection (OSI) reference model defined by the International Standards Organization (ISO)