svn commit: r44142 - head/en_US.ISO8859-1/books/handbook/advanced-networking
Dru Lavigne
dru at FreeBSD.org
Wed Mar 5 22:34:27 UTC 2014
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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