102 lines
4.8 KiB
HTML
102 lines
4.8 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>The services and protocols Files</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="node128.html">Remote Procedure Call</A>
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<B>Up:</B> <A HREF="node124.html">Various Network Applications</A>
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<B> Previous:</B> <A HREF="node126.html">The tcpd access control </A>
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<BR> <P>
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<H1><A NAME="SECTION0011300000">The services and protocols Files</A></H1>
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The port numbers on which certain ``standard'' services are offered are
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defined in the ``Assigned Numbers'' RFC. To enable server and client
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programs to convert service names to these numbers, at least a part of
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the list is kept on each host; it is stored in a file called
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/etc/services. An entry is made up like this:
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<pre>
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service port/protocol [aliases]
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</pre>
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Here, service specifies the service name, port defines the
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port the service is offered on, and protocol defines which
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transport protocol is used. Commonly, this is either udp or
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tcp. It is possible for a service to be offered for more
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than one protocol, as well as offering different services on the same
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port, as long as the protocols are different. The aliases field
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allows to specify alternative names for the same service.
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<P>
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Usually, you don't have to change the services file that comes along
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with the network software on your system. Nevertheless, we
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give a small excerpt from that file below.
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<pre>
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# The services file:
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#
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# well-known services
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echo 7/tcp # Echo
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echo 7/udp #
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discard 9/tcp sink null # Discard
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discard 9/udp sink null #
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daytime 13/tcp # Daytime
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daytime 13/udp #
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chargen 19/tcp ttytst source # Character Generator
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chargen 19/udp ttytst source #
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ftp-data 20/tcp # File Transfer Protocol (Data)
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ftp 21/tcp # File Transfer Protocol (Contr
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telnet 23/tcp # Virtual Terminal Protocol
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smtp 25/tcp # Simple Mail Transfer Protocol
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nntp 119/tcp readnews # Network News Transfer Protoco
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#
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# UNIX services
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exec 512/tcp # BSD rexecd
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biff 512/udp comsat # mail notification
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login 513/tcp # remote login
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who 513/udp whod # remote who and uptime
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shell 514/tcp cmd # remote command, no passwd use
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syslog 514/udp # remote system logging
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printer 515/tcp spooler # remote print spooling
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route 520/udp router routed # routing information protocol
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</pre>
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Note that, for example, the echo service is offered on
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port 7 for both TCP and UDP, and that port 512 is used for two different
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services, namely the COMSAT daemon (which notifies users of newly
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arrived mail, see xbiff(1x)), over UDP, and for remote
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execution (rexec(1)), using TCP.
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<P>
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<A NAME="4743"></A>
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Similar to the services file, the networking library needs a way to
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translate protocol names--- for example, those used in the services
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file--- to protocol numbers understood by the IP layer on other hosts.
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This is done by looking up the name in the /etc/protocols file.
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It contains one entry per line, each containing a protocol name, and the
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associated number. Having to touch this file is even more unlikely than
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having to meddle with /etc/services. A sample file is given
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below:
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</pre>
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#
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# Internet (IP) protocols
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#
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ip 0 IP # internet protocol, pseudo protocol
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icmp 1 ICMP # internet control message protocol
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igmp 2 IGMP # internet group multicast protocol
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tcp 6 TCP # transmission control protocol
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udp 17 UDP # user datagram protocol
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raw 255 RAW # RAW IP interface
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<pre>
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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="node128.html">Remote Procedure Call</A>
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<B>Up:</B> <A HREF="node124.html">Various Network Applications</A>
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<B> Previous:</B> <A HREF="node126.html">The tcpd access control </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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