Date: Wed, 5 Mar 2014 22:34:27 +0000 (UTC) From: Dru Lavigne <dru@FreeBSD.org> To: doc-committers@freebsd.org, svn-doc-all@freebsd.org, svn-doc-head@freebsd.org Subject: svn commit: r44142 - head/en_US.ISO8859-1/books/handbook/advanced-networking Message-ID: <201403052234.s25MYRaD040287@svn.freebsd.org>
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Author: dru Date: Wed Mar 5 22:34:26 2014 New Revision: 44142 URL: http://svnweb.freebsd.org/changeset/doc/44142 Log: Editorial pass through Routing Basics. Add name to table. Sponsored by: iXsystems Modified: head/en_US.ISO8859-1/books/handbook/advanced-networking/chapter.xml Modified: head/en_US.ISO8859-1/books/handbook/advanced-networking/chapter.xml ============================================================================== --- head/en_US.ISO8859-1/books/handbook/advanced-networking/chapter.xml Wed Mar 5 21:39:21 2014 (r44141) +++ head/en_US.ISO8859-1/books/handbook/advanced-networking/chapter.xml Wed Mar 5 22:34:26 2014 (r44142) @@ -132,7 +132,7 @@ Routing tables Internet: Destination Gateway Flags Refs Use Netif Expire -default outside-gw UGSc 37 418 em0 +default outside-gw UGS 37 418 em0 localhost localhost UH 0 181 lo0 test0 0:e0:b5:36:cf:4f UHLW 5 63288 re0 77 10.20.30.255 link#1 UHLW 1 2421 @@ -148,33 +148,37 @@ host2.example.com link#1 UC <varlistentry> <term>default</term> <listitem> - <para>The first line specifies the <literal></literal> + <para>The first route in this table specifies the <literal>default</literal> route. When the local system needs to make a connection to a remote host, it checks the routing table to determine if a - known path exists. If the remote host falls into a subnet - that it knows how to reach, the system checks to see if it - can connect using that interface.</para> - - <para>If all known paths fail, the system has one last option: - the <quote>default</quote> route. This route is a special - type of gateway route (usually the only one present in the - system), and is always marked with a <literal>c</literal> in - the flags field. For hosts on a local area network, this - gateway is set to the system which has a direct connection to - the Internet.</para> + known path exists. If the remote host matches an entry in the + table, the system checks to see if it + can connect using the interface specified in that entry.</para> + + <para>If the destination does not match an entry, or if all known + paths fail, the system uses the entry for the + default route. For hosts on a local area network, the + <literal>Gateway</literal> field in the default route is set + to the system which has a direct connection to + the Internet. When reading this entry, verify that the + <literal>Flags</literal> column indicates that the gateway is + usable (<literal>UG</literal>).</para> + <para>The default route for a machine which itself is + functioning as the gateway to the outside world will be the + gateway machine at the Internet Service Provider + (<acronym>ISP</acronym>).</para> </listitem> </varlistentry> <varlistentry> <term>localhost</term> <listitem> - <para>The second line is the <literal>localhost</literal> route. - The interface (<literal>Netif</literal> column) that this - routing table specifies to use for - <literal>localhost</literal> is <filename>lo0</filename>, - also known as the loopback device. This says to keep all - traffic for this destination internal, rather than sending it + <para>The second route is the <literal>localhost</literal> route. + The interface specified in the <literal>Netif</literal> column + for <literal>localhost</literal> is <filename>lo0</filename>, + also known as the loopback device. This indicates that all + traffic for this destination should be internal, rather than sending it out over the network.</para> </listitem> </varlistentry> @@ -201,8 +205,8 @@ host2.example.com link#1 UC <varlistentry> <term>subnet</term> <listitem> - <para>&os; will add subnet routes for the local subnet. - <systemitem class="ipaddress">10.20.30.255</systemitem> is the + <para>&os; will automatically add subnet routes for the local subnet. + In this example, <systemitem class="ipaddress">10.20.30.255</systemitem> is the broadcast address for the subnet <systemitem class="ipaddress">10.20.30</systemitem> and <systemitem class="fqdomainname">example.com</systemitem> is the domain @@ -231,7 +235,7 @@ host2.example.com link#1 UC <literal>=></literal> symbol after the <filename>lo0</filename> interface says that an alias has been set in addition to the loopback address. Such routes only - show up on the host that supports the alias; all other hosts + show up on the host that supports the alias and all other hosts on the local network will have a <literal>link#1</literal> line for such routes.</para> </listitem> @@ -248,177 +252,80 @@ host2.example.com link#1 UC </variablelist> <para>Various attributes of each route can be seen in - the <literal>Flags</literal> column. Below is a short table - of some of these flags and their meanings:</para> + the <literal>Flags</literal> column. <xref linkend="routeflags"/> + summarizes some of these flags and their meanings:</para> + + <table xml:id="routeflags" frame="none" pgwide="1"> + <title>Commonly Seen Routing Table Flags</title> - <informaltable frame="none" pgwide="1"> <tgroup cols="2"> - <colspec colwidth="1*"/> - <colspec colwidth="4*"/> + <thead> + <row> + <entry>Command</entry> + <entry>Purpose</entry> + </row> + </thead> <tbody> <row> <entry>U</entry> - <entry>Up: The route is active.</entry> + <entry>The route is active (up).</entry> </row> <row> <entry>H</entry> - <entry>Host: The route destination is a single + <entry>The route destination is a single host.</entry> </row> <row> <entry>G</entry> - <entry>Gateway: Send anything for this destination on to - this remote system, which will figure out from there + <entry>Send anything for this destination on to + this gateway, which will figure out from there where to send it.</entry> </row> <row> <entry>S</entry> - <entry>Static: This route was configured manually, not - automatically generated by the system.</entry> + <entry>This route was statically configured.</entry> </row> <row> <entry>C</entry> - <entry>Clone: Generates a new route based upon this + <entry>Clones a new route based upon this route for machines to connect to. This type of route is normally used for local networks.</entry> </row> <row> <entry>W</entry> - <entry>WasCloned: Indicated a route that was + <entry>The route was auto-configured based upon a local area network - (Clone) route.</entry> + (clone) route.</entry> </row> <row> <entry>L</entry> - <entry>Link: Route involves references to Ethernet + <entry>Route involves references to Ethernet (link) hardware.</entry> </row> </tbody> </tgroup> - </informaltable> - - <para>The default route for a machine which itself is - functioning as the gateway to the outside world, will be the - gateway machine at the Internet Service Provider - (<acronym>ISP</acronym>).</para> - - <para>This example is a common configuration for a default - route:</para> - - <mediaobject> - <imageobject> - <imagedata fileref="advanced-networking/net-routing"/> - </imageobject> - - <textobject> - <literallayout class="monospaced"> -[Local2] <--ether--> [Local1] <--PPP--> [ISP-Serv] <--ether--> [T1-GW]</literallayout> - </textobject> - </mediaobject> - - <para>The hosts <systemitem>Local1</systemitem> and - <systemitem>Local2</systemitem> are on the local network. - <systemitem>Local1</systemitem> is connected to an - <acronym>ISP</acronym> using a - <acronym>PPP</acronym> connection. This - <acronym>PPP</acronym> server is connected through a local - area network to another gateway computer through an external - interface to the <acronym>ISP</acronym>.</para> - - <para>The default routes for each machine will be:</para> - - <informaltable frame="none" pgwide="1"> - <tgroup cols="3"> - <thead> - <row> - <entry>Host</entry> - <entry>Default Gateway</entry> - <entry>Interface</entry> - </row> - </thead> - - <tbody> - <row> - <entry>Local2</entry> - <entry>Local1</entry> - <entry>Ethernet</entry> - </row> - - <row> - <entry>Local1</entry> - <entry>T1-GW</entry> - <entry>PPP</entry> - </row> - </tbody> - </tgroup> - </informaltable> - - <para>A common question is <quote>Why is - <systemitem>T1-GW</systemitem> configured as the default - gateway for <systemitem>Local1</systemitem>, rather than the - <acronym>ISP</acronym> server it is connected - to?</quote>.</para> - - <para>Since the <acronym>PPP</acronym> interface is using an - address on the <acronym>ISP</acronym>'s local network for the - local side of the connection, routes for any other machines on - the <acronym>ISP</acronym>'s local network will be - automatically generated. The system already knows how to - reach the <systemitem>T1-GW</systemitem> machine, so there is - no need for the intermediate step of sending traffic to the - <acronym>ISP</acronym>'s server.</para> - - <para>It is common to use the address <systemitem - class="ipaddress">X.X.X.1</systemitem> as the gateway - address for the local network. So, if the local class C - address space is <systemitem - class="ipaddress">10.20.30</systemitem> and the - <acronym>ISP</acronym> is using <systemitem - class="ipaddress">10.9.9</systemitem>, the default routes - would be:</para> - - <informaltable frame="none" pgwide="1"> - <tgroup cols="2"> - <thead> - <row> - <entry>Host</entry> - <entry>Default Route</entry> - </row> - </thead> - <tbody> - <row> - <entry>Local2 (10.20.30.2)</entry> - <entry>Local1 (10.20.30.1)</entry> - </row> - - <row> - <entry>Local1 (10.20.30.1, 10.9.9.30)</entry> - <entry>T1-GW (10.9.9.1)</entry> - </row> - </tbody> - </tgroup> - </informaltable> + </table> - <para>The default route can be easily defined in - <filename>/etc/rc.conf</filename>. In this example, on - <systemitem>Local2</systemitem>, add the following line to - <filename>/etc/rc.conf</filename>:</para> + <para>On a &os; system, the default route can defined in + <filename>/etc/rc.conf</filename> by specifying the + <acronym>IP</acronym> address of the default gateway:</para> <programlisting>defaultrouter="10.20.30.1"</programlisting> - <para>It is also possible to add the route directly using - &man.route.8;:</para> + <para>It is also possible to manually add the route using + <command>route</command>:</para> <screen>&prompt.root; <userinput>route add default 10.20.30.1</userinput></screen> - <para>For more information on manual manipulation of network + <para>Note that manually added routes will not survive a reboot. + For more information on manual manipulation of network routing tables, refer to &man.route.8;.</para> </sect2>
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