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Editorial pass through Routing Basics.

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Add name to table.

Sponsored by: iXsystems
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Dru Lavigne 2014-03-05 22:34:26 +00:00
parent 7ada9725e0
commit 61eb3b5669
Notes: svn2git 2020-12-08 03:00:23 +00:00 
svn path=/head/; revision=44142
1 changed files with 53 additions and 146 deletions
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en_US.ISO8859-1/books/handbook/advanced-networking/chapter.xml
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@ -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 0 0
<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>
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 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>
<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 0 0
<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 0 0
<literal>=&gt;</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 0 0
</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>
</table>
<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] &lt;--ether--&gt; [Local1] &lt;--PPP--&gt; [ISP-Serv] &lt;--ether--&gt; [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>
<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>