dc1fbb135c
e.g. sysctl instead of the GATEWAY option
use a refer instead of an old file (options.info)
503 lines
20 KiB
Plaintext
503 lines
20 KiB
Plaintext
<!-- This is an SGML version in the linuxdoc DTD of the SLIP Server
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FAQ by Guy Helmer.
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This guide provides instruction in configuring and preparing
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a FreeBSD system to be a dialup SLIP server.
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<title>
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Setting up FreeBSD as a SLIP Server
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<author>Guy Helmer, <tt/ghelmer@alpha.dsu.edu/
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<date>v1.0, 15 May 1995
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-->
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<sect><heading>Setting up a SLIP server<label id="slips"></heading>
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<p><em>Contribudted by &a.ghelmer;.<newline>
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v1.0, 15 May 1995.</em>
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This document provides suggestions for setting up SLIP Server services
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on a FreeBSD system, which typically means configuring your system to
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automatically startup connections upon login for remote SLIP clients.
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The author has written this document based on his experience;
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however, as your system and needs may be different, this document may
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not answer all of your questions, and the author cannot be responsible
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if you damage your system or lose data due to attempting to follow the
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suggestions here.
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This guide was originally written for SLIP Server services on a
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FreeBSD 1.x system. It has been modified to reflect changes in the
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pathnames and the removal of the SLIP interface compression flags in
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early versions of FreeBSD 2.X, which appear to be the only major
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changes between FreeBSD versions. If you do encounter mistakes in
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this document, please email the author with enough information to
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help correct the problem.
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<sect1><heading>Prerequisites<label id="slips:prereqs"></>
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<p>
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This document is very technical in nature, so background knowledge is
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required. It is assumed that you are familiar with the TCP/IP network
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protocol, and in particular, network and node addressing, network
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address masks, subnetting, routing, and routing protocols, such as
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RIP. Configuring SLIP services on a dial-up server requires a
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knowledge of these concepts, and if you are not familiar with them,
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please read a copy of either Craig Hunt's <em>TCP/IP Network
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Administration</em> published by O'Reilly & Associates, Inc. (ISBN
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Number 0-937175-82-X), or Douglas Comer's books on the TCP/IP
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protocol.
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It's further assumed that you have already setup your modem(s) and
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configured the appropriate system files to allow logins through your
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modems. If you haven't prepared your system for this yet, please see
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the tutorial for configuring dialup services; if you have a World-Wide
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Web browser available, browse the list of tutorials at
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<tt>http://www.freebsd.org/</tt>; otherwise, check the place
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where you found this document for a document named <tt/dialup.txt/ or
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something similar. You may also want to check the manual pages for
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<tt/sio(4)/ for information on the serial port device driver and
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<tt/ttys(5)/, <tt/gettytab(5)/, <tt/getty(8)/, & <tt/init(8)/ for
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information relevant to configuring the system to accept logins on
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modems, and perhaps <tt/stty(1)/ for information on setting serial
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port parameters [such as <tt/clocal/ for directly-connected
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serial interfaces].
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<sect1><heading>Quick Overview</heading>
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<p>
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In its typical configuration, using FreeBSD as a SLIP server works as
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follows: a SLIP user dials up your FreeBSD SLIP Server system and logs
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in with a special SLIP login ID that uses <tt>/usr/sbin/sliplogin</tt>
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as the special user's shell. The <tt/sliplogin/ program browses the
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file <tt>/etc/sliphome/slip.hosts</tt> to find a matching line for
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the special user, and if it finds a match, connects the serial line to
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an available SLIP interface and then runs the shell script
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<tt>/etc/sliphome/slip.login</tt> to configure the SLIP interface.
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<sect2><heading>An Example of a SLIP Server Login</heading>
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<p>
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For example, if a SLIP user ID were <tt>Shelmerg</tt>, <tt/Shelmerg/'s
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entry in <tt>/etc/master.passwd</tt> would look something like this
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(except it would be all on one line):
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<tscreen><verb>
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Shelmerg:password:1964:89::0:0:Guy Helmer - SLIP:
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/usr/users/Shelmerg:/usr/sbin/sliplogin
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</verb></tscreen>
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and, when <tt/Shelmerg/ logs in, <tt>sliplogin</tt> will search
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<tt>/etc/sliphome/slip.hosts</tt> for a line that had a matching user
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ID; for example, there may be a line in
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<tt>/etc/sliphome/slip.hosts</tt> that reads:
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<tscreen><verb>
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Shelmerg dc-slip sl-helmer 0xfffffc00 autocomp
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</verb></tscreen>
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<tt/sliplogin/ will find that matching line, hook the serial line into
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the next available SLIP interface, and then execute
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<tt>/etc/sliphome/slip.login</tt> like this:
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<tscreen><verb>
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/etc/sliphome/slip.login 0 19200 Shelmerg dc-slip sl-helmer 0xfffffc00 autocomp
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</verb></tscreen>
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If all goes well, <tt>/etc/sliphome/slip.login</tt> will issue an
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<tt>ifconfig</tt> for the SLIP interface to which <tt/sliplogin/
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attached itself (slip interface 0, in the above example, which was the
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first parameter in the list given to <tt>slip.login</tt>) to set the
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local IP address (<tt>dc-slip</tt>), remote IP address
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(<tt>sl-helmer</tt>), network mask for the SLIP interface
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(<tt>0xfffffc00</tt>), and any additional flags (<tt>autocomp</tt>).
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If something goes wrong, <tt/sliplogin/ usually logs good
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informational messages via the daemon syslog facility, which usually
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goes into <tt>/var/log/messages</tt> (see the manual pages for
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<tt>syslogd(8)</tt> and <tt>syslog.conf(5)</tt>, and perhaps check
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<tt>/etc/syslog.conf</tt> to see to which files <tt>syslogd</tt> is
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logging).
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OK, enough of the examples -- let's dive into setting up the system.
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<sect1><heading>Kernel Configuration</heading>
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<p>
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FreeBSD's default kernels usually come with two SLIP interfaces
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defined (<tt>sl0</tt> and <tt>sl1</tt>); you can use <tt>netstat
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-i</tt> to see whether these interfaces are defined in your kernel.
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Sample output from <tt>netstat -i</tt>:
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<tscreen><verb>
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Name Mtu Network Address Ipkts Ierrs Opkts Oerrs Coll
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ed0 1500 <Link>0.0.c0.2c.5f.4a 291311 0 174209 0 133
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ed0 1500 138.247.224 ivory 291311 0 174209 0 133
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lo0 65535 <Link> 79 0 79 0 0
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lo0 65535 loop localhost 79 0 79 0 0
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sl0* 296 <Link> 0 0 0 0 0
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sl1* 296 <Link> 0 0 0 0 0
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</verb></tscreen>
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The <tt>sl0</tt> and <tt>sl1</tt> interfaces shown in <tt>netstat
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-i</tt>'s output indicate that there are two SLIP interfaces built
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into the kernel. (The asterisks after the <tt>sl0</tt> and
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<tt>sl1</tt> indicate that the interfaces are ``down''.)
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However, FreeBSD's default kernels do not come configured to forward
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packets (ie, your FreeBSD machine will not act as a router) due to
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Internet RFC requirements for Internet hosts (see RFC's 1009
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[Requirements for Internet Gateways], 1122
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[Requirements for Internet Hosts -- Communication Layers],
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and perhaps 1127 [A Perspective on the Host Requirements
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RFCs]), so if you want your FreeBSD SLIP Server to act as a
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router, you'll have to add the line
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<verb>
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sysctl -w net.inet.ip.forwarding = 0
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</verb>
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to your rc.local file.
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You'll notice that near the end of the default kernel configuration
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file (<tt>/sys/i386/conf/GENERIC</tt>) is a line that reads:
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<tscreen><verb>
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pseudo-device sl 2
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</verb></tscreen>
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which is the line that defines the number of SLIP devices available in
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the kernel; the number at the end of the line is the maximum number of
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SLIP connections that may be operating simultaneously.
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Please refer to <ref id="kernelconfig" name="Configuring the FreeBSD Kernel">
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for help in reconfiguring your kernel.
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<sect1><heading>Sliplogin Configuration</heading>
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<p>
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As mentioned earlier, there are three files in the
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<tt>/etc/sliphome</tt> directory that are part of the configuration
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for <tt>/usr/sbin/sliplogin</tt> (see <tt>sliplogin(8)</tt> for the
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actual manual page for <tt>sliplogin</tt>): <tt>slip.hosts</tt>, which
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defines the SLIP users & their associated IP addresses;
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<tt>slip.login</tt>, which usually just configures the SLIP interface;
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and (optionally) <tt>slip.logout</tt>, which undoes
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<tt>slip.login</tt>'s effects when the serial connection is
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terminated.
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<sect2><heading>slip.hosts Configuration</heading>
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<p>
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<tt>/etc/sliphome/slip.hosts</tt> contains lines which have at least
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four items, separated by whitespace:
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<itemize>
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<item> SLIP user's login ID
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<item> Local address (local to the SLIP server) of the SLIP link
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<item> Remote address of the SLIP link
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<item> Network mask
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</itemize>
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The local and remote addresses may be host names (resolved to IP
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addresses by <tt>/etc/hosts</tt> or by the domain name service,
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depending on your specifications in <tt>/etc/host.conf</tt>), and I
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believe the network mask may be a name that can be resolved by a
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lookup into <tt>/etc/networks</tt>. On a sample system,
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<tt>/etc/sliphome/slip.hosts</tt> looks like this:
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<tscreen><verb>
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----- begin /etc/sliphome/slip.hosts -----
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#
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# login local-addr remote-addr mask opt1 opt2
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# (normal,compress,noicmp)
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#
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Shelmerg dc-slip sl-helmerg 0xfffffc00 autocomp
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----- end /etc/sliphome/slip.hosts ------
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</verb></tscreen>
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At the end of the line is one or more of the options.
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<itemize>
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<item> <tt>normal</tt> - no header compression
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<item> <tt>compress</tt> - compress headers
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<item> <tt>autocomp</tt> - compress headers if the remote end allows it
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<item> <tt>noicmp</tt> - disable ICMP packets (so any ``ping'' packets will be
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dropped instead of using up your bandwidth)
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</itemize>
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Note that <tt/sliplogin/ under early releases of FreeBSD 2 ignored
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the options that FreeBSD 1.x recognized, so the options
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<tt/normal/, <tt/compress/, <tt/autocomp/, and <tt/noicmp/ had no effect
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until support was added in FreeBSD 2.2 (unless your <tt/slip.login/ script
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included code to make use of the flags).
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Your choice of local and remote addresses for your SLIP links depends
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on whether you are going to dedicate a TCP/IP subnet or if you are
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going to use ``proxy ARP'' on your SLIP server (it's not ``true''
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proxy ARP, but that is the terminology used in this document to
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describe it). If you're not sure which method to select or how to
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assign IP addresses, please refer to the TCP/IP books referenced in
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the <ref id="slips:prereqs"> section and/or consult your IP network manager.
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If you are going to use a separate subnet for your SLIP clients, you
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will need to allocate the subnet number out of your assigned IP
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network number and assign each of your SLIP client's IP numbers out of
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that subnet. Then, you will probably either need to configure a
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static route to the SLIP subnet via your SLIP server on your nearest
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IP router, or install <tt>gated</tt> on your FreeBSD SLIP server and
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configure it to talk the appropriate routing protocols to your other
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routers to inform them about your SLIP server's route to the SLIP
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subnet.
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Otherwise, if you will use the ``proxy ARP'' method, you will need to
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assign your SLIP client's IP addresses out of your SLIP server's
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Ethernet subnet, and you'll also need to adjust your
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<tt>/etc/sliphome/slip.login</tt> and
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<tt>/etc/sliphome/slip.logout</tt> scripts to use <tt>arp(8)</tt> to
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manage the proxy-ARP entries in the SLIP server's ARP table.
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<sect2><heading>slip.login Configuration</heading>
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<p>
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The typical <tt>/etc/sliphome/slip.login</tt> file looks like this:
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<tscreen><verb>
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----- begin /etc/sliphome/slip.login -----
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#!/bin/sh -
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#
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# @(#)slip.login 5.1 (Berkeley) 7/1/90
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#
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# generic login file for a slip line. sliplogin invokes this with
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# the parameters:
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# 1 2 3 4 5 6 7-n
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# slipunit ttyspeed loginname local-addr remote-addr mask opt-args
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#
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/sbin/ifconfig sl$1 inet $4 $5 netmask $6
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----- end /etc/sliphome/slip.login -----
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</verb></tscreen>
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This <tt>slip.login</tt> file merely ifconfig's the appropriate SLIP
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interface with the local and remote addresses and network mask of the
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SLIP interface.
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If you have decided to use the ``proxy ARP'' method (instead of using
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a separate subnet for your SLIP clients), your
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<tt>/etc/sliphome/slip.login</tt> file will need to look something
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like this:
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<tscreen><verb>
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----- begin /etc/sliphome/slip.login for "proxy ARP" -----
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#!/bin/sh -
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#
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# @(#)slip.login 5.1 (Berkeley) 7/1/90
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#
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# generic login file for a slip line. sliplogin invokes this with
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# the parameters:
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# 1 2 3 4 5 6 7-n
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# slipunit ttyspeed loginname local-addr remote-addr mask opt-args
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#
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/sbin/ifconfig sl$1 inet $4 $5 netmask $6
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# Answer ARP requests for the SLIP client with our Ethernet addr
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/usr/sbin/arp -s $5 00:11:22:33:44:55 pub
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----- end /etc/sliphome/slip.login for "proxy ARP" -----
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</verb></tscreen>
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The additional line in this <tt>slip.login</tt>, <tt>arp -s $5
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00:11:22:33:44:55 pub</tt>, creates an ARP entry in the SLIP server's
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ARP table. This ARP entry causes the SLIP server to respond with the
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SLIP server's Ethernet MAC address whenever a another IP node on the
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Ethernet asks to speak to the SLIP client's IP address.
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When using the example above, be sure to replace the Ethernet MAC
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address (<tt>00:11:22:33:44:55</tt>) with the MAC address of your
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system's Ethernet card, or your ``proxy ARP'' will definitely not work!
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You can discover your SLIP server's Ethernet MAC address by looking at
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the results of running <tt>netstat -i</tt>; the second line of the output
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should look something like:
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<tscreen><verb>
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ed0 1500 <Link>0.2.c1.28.5f.4a 191923 0 129457 0 116
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^^^^^^^^^^^^^^^
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</verb></tscreen>
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which indicates that this particular system's Ethernet MAC address is
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<tt>00:02:c1:28:5f:4a</tt> -- the periods in the Ethernet MAC address
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given by <tt>netstat -i</tt> must be changed to colons and leading zeros
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should be added to each single-digit hexadecimal number to convert the
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address into the form that <tt>arp(8)</tt> desires; see the manual page on
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<tt>arp(8)</tt> for complete information on usage.
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Note that when you create <tt>/etc/sliphome/slip.login</tt> and
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<tt>/etc/sliphome/slip.logout</tt>, the ``execute'' bit (ie,
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<tt>chmod 755 /etc/sliphome/slip.login
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/etc/sliphome/slip.logout</tt>) must be set, or <tt>sliplogin</tt>
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will be unable to execute it.
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<sect2><heading>slip.logout Configuration</heading>
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<p>
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<tt>/etc/sliphome/slip.logout</tt> isn't strictly needed (unless you
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are implementing ``proxy ARP''), but if you decide to create it, this
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is an example of a basic <tt>slip.logout</tt> script:
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<tscreen><verb>
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----- begin /etc/sliphome/slip.logout -----
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#!/bin/sh -
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#
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# slip.logout
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#
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# logout file for a slip line. sliplogin invokes this with
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# the parameters:
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# 1 2 3 4 5 6 7-n
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# slipunit ttyspeed loginname local-addr remote-addr mask opt-args
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#
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/sbin/ifconfig sl$1 down
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----- end /etc/sliphome/slip.logout -----
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</verb></tscreen>
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If you are using ``proxy ARP'', you'll want to have
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<tt>/etc/sliphome/slip.logout</tt> remove the ARP entry for the SLIP
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client:
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<tscreen><verb>
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----- begin /etc/sliphome/slip.logout for "proxy ARP" -----
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#!/bin/sh -
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#
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# @(#)slip.logout
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#
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# logout file for a slip line. sliplogin invokes this with
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# the parameters:
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# 1 2 3 4 5 6 7-n
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# slipunit ttyspeed loginname local-addr remote-addr mask opt-args
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#
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/sbin/ifconfig sl$1 down
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# Quit answering ARP requests for the SLIP client
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/usr/sbin/arp -d $5
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----- end /etc/sliphome/slip.logout for "proxy ARP" -----
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</verb></tscreen>
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The <tt>arp -d $5</tt> removes the ARP entry that the ``proxy ARP''
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<tt>slip.login</tt> added when the SLIP client logged in.
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It bears repeating: make sure <tt>/etc/sliphome/slip.logout</tt> has
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the execute bit set for after you create it (ie, <tt>chmod 755
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/etc/sliphome/slip.logout</tt>).
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<sect1><heading>Routing Considerations</heading>
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<p>
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|
If you are not using the ``proxy ARP'' method for routing packets
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|
between your SLIP clients and the rest of your network (and perhaps
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|
the Internet), you will probably either have to add static routes to
|
|
your closest default router(s) to route your SLIP client subnet via
|
|
your SLIP server, or you will probably need to install and configure
|
|
<tt>gated</tt> on your FreeBSD SLIP server so that it will tell your
|
|
routers via appropriate routing protocols about your SLIP subnet.
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<sect2><heading>Static Routes</heading>
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<p>
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|
Adding static routes to your nearest default routers can be
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troublesome (or impossible, if you don't have authority to do so...).
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|
If you have a multiple-router network in your organization, some
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|
routers, such as Cisco and Proteon, may not only need to be configured
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|
with the static route to the SLIP subnet, but also need to be told
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|
which static routes to tell other routers about, so some expertise and
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troubleshooting/tweaking may be necessary to get static-route-based
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routing to work.
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<sect2><heading>Running gated</heading>
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<p>
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An alternative to the headaches of static routes is to install
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<tt>gated</tt> on your FreeBSD SLIP server and configure it to use the
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appropriate routing protocols (RIP/OSPF/BGP/EGP) to tell other routers
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about your SLIP subnet. <tt/gated/ is available via anonymous ftp
|
|
from <tt>ftp.gated.cornell.edu</tt> in the directory
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<tt>/pub/gated</tt>; I believe the current version as of this writing
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|
is <tt>gated-R3_5Alpha_8.tar.Z</tt>, which includes support for
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FreeBSD ``out-of-the-box''. Complete information and documentation on
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<tt>gated</tt> is available on the Web starting at
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<tt>http://www.gated.cornell.edu/</tt>. Compile and install it, and
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then write a <tt>/etc/gated.conf</tt> file to configure your gated;
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|
here's a sample, similar to what the author used on a FreeBSD SLIP
|
|
server:
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|
|
|
<tscreen><verb>
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|
----- begin sample /etc/gated.conf for gated version 3.5Alpha5 -----
|
|
#
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|
# gated configuration file for dc.dsu.edu; for gated version 3.5alpha5
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|
# Only broadcast RIP information for xxx.xxx.yy out the ed Ethernet interface
|
|
#
|
|
#
|
|
# tracing options
|
|
#
|
|
traceoptions "/var/tmp/gated.output" replace size 100k files 2 general ;
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|
|
|
rip yes {
|
|
interface sl noripout noripin ;
|
|
interface ed ripin ripout version 1 ;
|
|
traceoptions route ;
|
|
} ;
|
|
|
|
#
|
|
# Turn on a bunch of tracing info for the interface to the kernel:
|
|
kernel {
|
|
traceoptions remnants request routes info interface ;
|
|
} ;
|
|
|
|
#
|
|
# Propagate the route to xxx.xxx.yy out the Ethernet interface via RIP
|
|
#
|
|
|
|
export proto rip interface ed {
|
|
proto direct {
|
|
xxx.xxx.yy mask 255.255.252.0 metric 1; # SLIP connections
|
|
} ;
|
|
} ;
|
|
|
|
#
|
|
# Accept routes from RIP via ed Ethernet interfaces
|
|
|
|
import proto rip interface ed {
|
|
all ;
|
|
} ;
|
|
|
|
----- end sample /etc/gated.conf -----
|
|
</verb></tscreen>
|
|
|
|
The above sample <tt>gated.conf</tt> file broadcasts routing
|
|
information regarding the SLIP subnet <tt>xxx.xxx.yy</tt> via RIP onto
|
|
the Ethernet; if you are using a different Ethernet driver than the
|
|
<tt/ed/ driver, you'll need to change the references to the <tt/ed/
|
|
interface appropriately. This sample file also sets up tracing to
|
|
<tt>/var/tmp/gated.output</tt> for debugging <tt>gated</tt>'s
|
|
activity; you can certainly turn off the tracing options if
|
|
<tt>gated</tt> works OK for you. You'll need to change the
|
|
<tt>xxx.xxx.yy</tt>'s into the network address of your own SLIP subnet
|
|
(be sure to change the net mask in the <tt>proto direct</tt> clause as
|
|
well).
|
|
|
|
When you get <tt>gated</tt> built and installed and create a
|
|
configuration file for it, you'll need to run <tt>gated</tt> in place
|
|
of <tt>routed</tt> on your FreeBSD system; change the
|
|
<tt>routed/gated</tt> startup parameters in <tt>/etc/netstart</tt> as
|
|
appropriate for your system. Please see the manual page for
|
|
<tt>gated</tt> for information on <tt>gated</tt>'s command-line
|
|
parameters.
|
|
|
|
<sect1><heading>Acknowledgements</heading>
|
|
|
|
<p>
|
|
Thanks to these people for comments and advice regarding this tutorial:
|
|
|
|
<descrip>
|
|
<tag/Wilko Bulte/ <wilko@yedi.iaf.nl>
|
|
<tag/Piero Serini/ <Piero@Strider.Inet.IT>
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|
</descrip>
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|
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<!-- </article> -->
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