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Finish editorial pass through Routing chapter.

Browse source 
The section on Multicast needs more content and a working
example.

Sponsored by: iXsystems
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Dru Lavigne 2014-03-06 02:08:27 +00:00
parent 61eb3b5669
commit 178e814996
Notes: svn2git 2020-12-08 03:00:23 +00:00 
svn path=/head/; revision=44143
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en_US.ISO8859-1/books/handbook/advanced-networking/chapter.xml
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@ -349,44 +349,30 @@ host2.example.com link#1 UC 0 0
<primary>dual homed hosts</primary>
</indexterm>
<para>A dual-homed system is a host which resides on two
different networks.</para>
<para>The dual-homed machine might have two Ethernet cards, each
having an address on a separate subnet. Alternately, the
machine can have one Ethernet card and uses &man.ifconfig.8;
aliasing. The former is used if two physically separate
Ethernet networks are in use and the latter if there is one
physical network segment, but two logically separate
subnets.</para>
<para>Either way, routing tables are set up so that each subnet
knows that this machine is the defined gateway (inbound route)
to the other subnet. This configuration, with the machine
acting as a router between the two subnets, is often used
to implement packet filtering or firewall security in
either or both directions.</para>
<para>For this machine to forward packets between the two
interfaces, &os; must be configured as a router, as
demonstrated in the next section.</para>
<para>A &os; system can be configured as the default gateway, or
router, for a network if it is a dual-homed system. A
dual-homed system is a host which resides on at least two
different networks. Typically, each network is connected to a separate
network interface, though <acronym>IP</acronym> aliasing can
be used to bind multiple addresses, each on a different
subnet, to one physical interface.</para>
<indexterm>
<primary>router</primary>
</indexterm>
<para>A network router is a system that forwards packets from
one interface to another. Internet standards and good
<para>In order for the system to forward packets between
interfaces, &os; must be configured as a router. Internet standards and good
engineering practice prevent the &os; Project from enabling
this by default in &os;. This feature can be enabled by
changing the following variable to <literal>YES</literal> in
&man.rc.conf.5;:</para>
this feature by default, but it can be configured to start at boot
by adding this line to
<filename>/etc/rc.conf</filename>:</para>
<programlisting>gateway_enable="YES" # Set to YES if this host will be a gateway</programlisting>
<para>This option will set the &man.sysctl.8; variable
<para>To enable routing now, set the &man.sysctl.8; variable
<varname>net.inet.ip.forwarding</varname> to
<literal>1</literal>. To stop routing, reset this to
<literal>1</literal>. To stop routing, reset this variable to
<literal>0</literal>.</para>
<indexterm>
@ -399,15 +385,24 @@ host2.example.com link#1 UC 0 0
<primary>OSPF</primary>
</indexterm>
<para>The new router will need routes to know where to send the
traffic. If the network is simple enough, static routes can
be used. &os; comes with the standard BSD routing daemon
&man.routed.8;, which speaks <acronym>RIP</acronym> versions
1 and 2, and <acronym>IRDP</acronym>. Support for
<acronym>BGP</acronym>v4, <acronym>OSPF</acronym>v2, and other
sophisticated routing protocols is available with the
<para>The routing table of a router needs additional routes so
it knows how to reach other networks. Routes can be either
added manually using
static routes or routes can be automatically learned using a routing protocol.
Static routes are appropriate for small networks and this
section describes how to add a static routing entry for a
small network.</para>
<note>
<para>For large networks, static routes quickly become
unscalable. &os; comes with the standard <acronym>BSD</acronym> routing daemon
&man.routed.8;, which provides the routing protocols <acronym>RIP</acronym>, versions
1 and 2, and <acronym>IRDP</acronym>. Support for the
<acronym>BGP</acronym> and <acronym>OSPF</acronym>
routing protocols can be installed using the
<package>net/zebra</package> package or
port.</para>
</note>
<para>Consider the following network:</para>
@ -449,12 +444,12 @@ host2.example.com link#1 UC 0 0
class="ipaddress">10.0.0.1</systemitem> which allows it to
connect with the outside world.
<systemitem>RouterB</systemitem> is already configured
properly as it uses <systemitem
class="ipaddress">192.168.1.1</systemitem> as the
to use <systemitem
class="ipaddress">192.168.1.1</systemitem> as its default
gateway.</para>
<para>The routing table on <systemitem>RouterA</systemitem>
looks something like this:</para>
<para>Before adding any static routes, the routing table on <systemitem>RouterA</systemitem>
looks like this:</para>
<screen>&prompt.user; <userinput>netstat -nr</userinput>
Routing tables
@ -467,45 +462,33 @@ default 10.0.0.1 UGS 0 49378 xl0
192.168.1.0/24 link#2 UC 0 0 xl1</screen>
<para>With the current routing table,
<systemitem>RouterA</systemitem> cannot reach Internal Net
2 as it does not have a route for <systemitem
class="ipaddress">192.168.2.0/24</systemitem>. The
following command adds the Internal Net 2 network to
<systemitem>RouterA</systemitem>
does not have a route to the <systemitem
class="ipaddress">192.168.2.0/24</systemitem> network. The
following command adds the <literal>Internal Net 2</literal> network to
<systemitem>RouterA</systemitem>'s routing table using
<systemitem class="ipaddress">192.168.1.2</systemitem> as
the next hop:</para>
<screen>&prompt.root; <userinput>route add -net 192.168.2.0/24 192.168.1.2</userinput></screen>
<para>Now <systemitem>RouterA</systemitem> can reach any hosts
<para>Now, <systemitem>RouterA</systemitem> can reach any host
on the <systemitem
class="ipaddress">192.168.2.0/24</systemitem>
network.</para>
<sect3>
<title>Persistent Configuration</title>
<para>The above example configures a static route on a
running system. However, the routing information will not
persist if the &os; system reboots. Persistent static
routes can be entered in
network. However, the routing information will not
persist if the &os; system reboots. If a static route needs
to be persistent, add it to
<filename>/etc/rc.conf</filename>:</para>
<programlisting># Add Internal Net 2 as a static route
<programlisting># Add Internal Net 2 as a persistent static route
static_routes="internalnet2"
route_internalnet2="-net 192.168.2.0/24 192.168.1.2"</programlisting>
<para>The <literal>static_routes</literal> configuration
variable is a list of strings separated by a space, where
each string references a route name. This example only
has one string in <literal>static_routes</literal>,
<replaceable>internalnet2</replaceable>. The variable
each string references a route name. The variable
<literal>route_internalnet2</literal>
contains all of the configuration parameters to
&man.route.8;. This example is equivalent to the
command:</para>
<screen>&prompt.root; <userinput>route add -net 192.168.2.0/24 192.168.1.2</userinput></screen>
contains the static route for that route name.</para>
<para>Using more than one string in
<literal>static_routes</literal> creates multiple static
@ -518,11 +501,10 @@ route_internalnet2="-net 192.168.2.0/24 192.168.1.2"</programlisting>
<programlisting>static_routes="net1 net2"
route_net1="-net 192.168.0.0/24 192.168.0.1"
route_net2="-net 192.168.1.0/24 192.168.1.1"</programlisting>
</sect3>
</sect2>
<sect2 xml:id="network-routing-propagation">
<title>Routing Propagation</title>
<sect2 xml:id="network-routing-troubleshooting">
<title>Troubleshooting</title>
<para>When an address space is assigned to a network, the
service provider configures their routing tables so that all
@ -537,38 +519,32 @@ route_net2="-net 192.168.1.0/24 192.168.1.1"</programlisting>
backbone machine has a copy of a master set of tables, which
direct traffic for a particular network to a specific
backbone carrier, and from there down the chain of service
providers until it reaches your network.</para>
providers until it reaches a particular network.</para>
<para>It is the task of the service provider to advertise to
the backbone sites that they are the point of connection, and
thus the path inward, for a site. This is known as route
propagation.</para>
</sect2>
<sect2 xml:id="network-routing-troubleshooting">
<title>Troubleshooting</title>
<indexterm>
<primary>&man.traceroute.8;</primary>
</indexterm>
<para>Sometimes, there is a problem with routing propagation
<para>Sometimes, there is a problem with route propagation
and some sites are unable to connect. Perhaps the most
useful command for trying to figure out where routing is
breaking down is &man.traceroute.8;. It is useful when
&man.ping.8; fails.</para>
breaking down is <command>traceroute</command>. It is useful when
<command>ping</command> fails.</para>
<para>When using &man.traceroute.8;, include the name of the
<para>When using <command>traceroute</command>, include the address of the
remote host to connect to. The output will show the gateway
hosts along the path of the attempt, eventually either
reaching the target host, or terminating because of a lack of
connection.</para>
<para>For more information, refer to &man.traceroute.8;.</para>
connection. For more information, refer to &man.traceroute.8;.</para>
</sect2>
<sect2 xml:id="network-routing-multicast">
<title>Multicast Routing</title>
<title>Multicast Considerations</title>
<indexterm>
<primary>multicast routing</primary>
@ -580,26 +556,29 @@ route_net2="-net 192.168.1.0/24 192.168.1.1"</programlisting>
<para>&os; natively supports both multicast applications and
multicast routing. Multicast applications do not require any
special configuration of &os;; as applications will generally
run out of the box. Multicast routing requires that support
special configuration in order to
run on &os;. Support for multicast routing requires that the
following option
be compiled into a custom kernel:</para>
<programlisting>options MROUTING</programlisting>
<para>The multicast routing daemon, &man.mrouted.8;, must be
configured to set up tunnels and <acronym>DVMRP</acronym> via
<filename>/etc/mrouted.conf</filename>. More details on
multicast configuration may be found in
&man.mrouted.8;.</para>
<para>The multicast routing daemon,
<application>mrouted</application> can be installed
using the <package>net/mrouted</package> package or port.
This daemon implements
the <acronym>DVMRP</acronym> multicast routing protocol and is
configured by editing <filename>/usr/local/etc/mrouted.conf</filename>
in order to set up the tunnels and <acronym>DVMRP</acronym>.
The installation of <application>mrouted</application> also installs
<application>map-mbone</application> and
<application>mrinfo</application>, as well as their associated
man pages. Refer to these for configuration examples.</para>
<note>
<para>The &man.mrouted.8; multicast routing daemon implements
the <acronym>DVMRP</acronym> multicast routing protocol,
which has largely been replaced by &man.pim.4; in many
multicast installations. &man.mrouted.8; and the related
&man.map-mbone.8; and &man.mrinfo.8; utilities are available
in the &os; Ports&nbsp;Collection as
<package>net/mrouted</package>.</para>
<para><acronym>DVMRP</acronym> has largely been replaced by the
<acronym>PIM</acronym> protocol in many
multicast installations. Refer to &man.pim.4; for more information.</para>
</note>
</sect2>
</sect1>