145 lines
5.9 KiB
HTML
145 lines
5.9 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
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<!--Converted with LaTeX2HTML 96.1-c (Feb 29, 1996) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds -->
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<HTML>
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<HEAD>
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<TITLE>Kernel Options in 1.1.14 and Higher</TITLE>
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</HEAD>
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<BODY LANG="EN">
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<A HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="contents_motif.gif"></A> <BR>
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<B> Next:</B> <A HREF="node46.html">A Tour of Network </A>
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<B>Up:</B> <A HREF="node43.html">Kernel Configuration</A>
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<B> Previous:</B> <A HREF="node44.html">Kernel Options in 1.0 </A>
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<BR> <P>
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<H2><A NAME="SECTION005220000">Kernel Options in 1.1.14 and Higher</A></H2>
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<P>
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Starting with 1.1.14, which added alpha support for IPX,
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the configuration procedure changed slightly. The general options section
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now asks whether you want networking support in general. It is
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immediately followed by a couple of question on miscellaneous
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networking options.
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<P>
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<P><P>
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<P>
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To use TCP/IP networking, you must answer this question with
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y. If you answer with n, however, you will still
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be able to compile the kernel with IPX support.
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<P>
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<P><P>
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<P>
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<A NAME="1955"></A>
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<A NAME="1956"></A>
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You have to enable this option if your system acts as a
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gateway between two Ethernets, or between and Ethernet and a
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SLIP link, etc. Although it doesn't hurt to enable this by
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default, you may want to disable this to configure a host as a
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so-called firewall. Firewalls are hosts that are connected to
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two or more networks, but don't route traffic between them.
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They are commonly used to provide users from a company network
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with Internet access at a minimal risk to the internal
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network. Users will be allowed to log into the firewall and
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use Internet services, but the company's machines will be
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protected from outside attacks because any incoming
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connections can't cross the firewall.
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<P>
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<P><P>
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<P>
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<A NAME="1959"></A>
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This option works around an incompatibility with some versions
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of PC/TCP, a commercial TCP/IP implementation for DOS-based
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PCs. If you enable this option, you will still be able to
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communicate with normal machines, but performance may
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be hurt over slow links.
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<P>
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<P><P>
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<P>
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<A NAME="1963"></A>
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This function enables RARP, the Reverse Address Resolution
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Protocol. RARP is used by diskless clients and X-terminals to
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inquire their IP-address when booting. You should enable RARP
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only when you plan to serve this sort of clients. The latest
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package of network utilities (net-0.32d) contains a small
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utility named rarp that allows you to add systems to the
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RARP cache.
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<P>
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<P><P>
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<P>
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<A NAME="1968"></A>
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<A NAME="1969"></A>
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<A NAME="1970"></A>
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<A NAME="1971"></A>
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<A NAME="2207"></A>
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When sending data over TCP, the kernel has to break up the
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stream into several packets before giving it to IP. For hosts
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that can be reached over a local network such as an Ethernet,
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larger packets will be used than for hosts where data has to
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go through long-distance links.<A HREF="footnode.html#1973"><IMG ALIGN=BOTTOM ALT="gif" SRC="foot_motif.gif"></A> If you don't enable SNARL, the kernel will assume
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only those networks are local that it actually has an interface
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to. However, if you look at the class B network at Groucho
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Marx University, the whole class B network is local, but most
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hosts interface to only one or two subnets. If you enable
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SNARL, the kernel will assume <em>all</em> subnets
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are local and use large packets when talking to all hosts on
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campus.
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<P>
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If you do want to use smaller packet sizes for data sent to
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specific hosts (because, for instance, the data goes through
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a SLIP link), you can do so using the mtu option of
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route, which is briefly discussed at the end of this
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chapter.
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<P>
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<P><P>
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<P>
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<A NAME="1981"></A>
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<A NAME="1982"></A>
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<A NAME="1983"></A>
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<A NAME="1984"></A>
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Nagle's rule is a heuristic to avoid sending particularly
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small IP packets, also called tinygrams. Tinygrams are usually
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created by interactive networking tools that transmit single
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keystrokes, such as telnet or rsh. Tinygrams can
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become particularly wasteful on low-bandwidth links like SLIP.
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The Nagle algorithm attempts to avoid them by holding back
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transmission of TCP data briefly under some circumstances. You
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might only want to disable Nagle's algorithm if you have
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severe problems with packets getting dropped.
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<P>
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<P><P>
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<P>
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<A NAME="1989"></A>
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<A NAME="1990"></A>
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<A NAME="1991"></A>
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This enables support for IPX, the transport protocol used by
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Novell Networking. It is still under development, and isn't
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really useful yet. One benefit of this will be that you can
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exchange data with IPX-based DOS utilities one day, and route
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traffic between your Novell-based networks through a PPP link.
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Support for the high-level protocols of Novell
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networking is however not in sight, as the specifications for
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these are available only at horrendous cost and under a
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non-disclosure agreement.
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<P>
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Starting in the 1.1.16 kernel, supports another
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driver type, the dummy driver. The following question appears
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toward the start of the device driver section.
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<P>
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<P><P>
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<P>
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The dummy driver doesn't really do much, but is quite useful
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on standalone or SLIP hosts. It is basically a masqueraded
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loopback interface. The reason to have this sort of interface
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is that on hosts that do SLIP but have no Ethernet, you want to
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have an interface that bears your IP address all the time.
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This is discussed in a little more detail in
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section-<A HREF="#ifaceinterfacedummy"><IMG ALIGN=BOTTOM ALT="gif" SRC="cross_ref_motif.gif"></A> in chapter-<A HREF="node58.html#iface"><IMG ALIGN=BOTTOM ALT="gif" SRC="cross_ref_motif.gif"></A>.
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<P>
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<HR><A HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="contents_motif.gif"></A> <BR>
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<B> Next:</B> <A HREF="node46.html">A Tour of Network </A>
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<B>Up:</B> <A HREF="node43.html">Kernel Configuration</A>
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<B> Previous:</B> <A HREF="node44.html">Kernel Options in 1.0 </A>
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<P><ADDRESS>
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<I>Andrew Anderson <BR>
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Thu Mar 7 23:22:06 EST 1996</I>
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</ADDRESS>
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</BODY>
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</HTML>
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