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Spelling: RoutingHowTo
* Introduction [1]
* Configuring IP forwarding [2]
* Linux [3]
* BSD variants (including MAC OSX) [4]
* Windows [5]
* Looking at the routing table [6]
* Default route [7]
* Links [8]
INTRODUCTION
So, you have this radio network thing and after playing with it for a
while you come to realize that you don't really want to bridge your
home network to the rest of the Melbourne Wireless community. You need
to set up a router. The router will do two things for you, it gives
you the control to expose the right amount of your network and it
allows you to establish a firewall between yourself and the general
Melbourne Wireless network. This is exactly the same as you would have
for your Internet connection.
The router may be an embedded device, a combination device
(router/wireless access point), a dedicated Linux machine (old PC) or
an existing machine you make dual homed by adding an additional NIC.
Regardless of the device you are using it needs to have more than one
network interface, should be able to forward packets between the
interfaces and should allow you to run firewall software and a routing
daemon or two. It's probably a good idea to have a dedicated machine
between you own stuff and the rest of the world, usual disclaimer
here.
CONFIGURING IP FORWARDING
Most PC based operating systems support ip forwarding but it is
usually not turned on. When you have a PC that has more than one
network interface and you want to enable routing, you may need to make
some simple configuration changes to get the machine forwarding
packets between interfaces.
Often you have the funny situation where the machine you want to act
as a router can see other machines on both subnets but machines on one
subnet cannot see machines on the other - you need to enable IP
forwarding.
LINUX
Most standard distributions support IP forwarding. you turn IP
forwarding on by setting a flag in _/proc_. This can be done using the
SYSCTL command or by simply echoing 1 to the file.
echo "1" > /proc/net/ipv4/ip_forward
Alternatively use SYSCTL
/sbin/sysctl -a will display all configured settings /sbin/sysctl
net.ipv4.ip_forward net.ipv4.ip_forward = 0 /sbin/sysctl -w
net.ipv4.ip_forward="1"
BSD VARIANTS (INCLUDING MAC OSX)
Similar to Linux, use sysctl to set the ip forwarding flag. In this
case the flag is _net.inet.ip.forwarding_.
/sbin/sysctl -w net.inet.ip.forwarding="1"
WINDOWS
In windows routing is possible through a change to a registry
parameter. Open regedit and go to the entry:
HKEY_LOCAL_MACHINE SYSTEMCurrentControlSetServicesTcpipParameters
Find the entry _IPEnableRouter_ and set to 1 (default is 0). Reboot
and you should be forwarding packets.
LOOKING AT THE ROUTING TABLE
The routing table can be inspected using the ROUTE command.
[dna@koen dna]$ /sbin/route Kernel IP routing table Destination
Gateway Genmask Flags Metric Ref Use Iface 192.168.1.3 *
255.255.255.255 UH 0 0 0 eth0 wailea * 255.255.255.255 UH 0 0 0 eth0
192.168.2.0 192.168.1.3 255.255.255.0 UG 0 0 0 eth0 192.168.2.0 wailea
255.255.255.0 UG 0 0 0 eth0 192.168.1.0 * 255.255.255.0 U 0 0 0 eth0
127.0.0.0 * 255.0.0.0 U 0 0 0 lo default bgenki2 0.0.0.0 UG 0 0 0 eth0
You can see different types of routing entries. Some are for machines
and others are for subnets. The machine entries are fully qualified
addresses or a machine name (192.168.1.3 or wailea) while the subnets
(in this case) are those that end in zero (192.168.2.0). Routes to
subnets include the IP Address of the gateway that is used to send
packets to the subnet. Typically you need to add a route to the
gateway first, then add the route to the subnet using the previously
defined gateway. There are exceptions to this, MAC OS X will add the
gateway automatically and has a different command syntax.
Alternative commands can access the same information but most likely
formatted differently. The raw routing data is maintained by the
kernel and is accessed by these commands from _/proc/net/route_.
/sbin/ip route (or /sbin/ip r) /bin/netstat -r
DEFAULT ROUTE
The default route is the route used for all packets that do not match
an explicitly defined route. Each device can have only one default
route. Each OS will have a slightly different command syntax for
creating a route. The same command usually allows you to look at the
routing table as well as set routes. This needs to be done as root or
a user with the appropriate permissions.
Linux
route add -net default 192.168.1.1 netmask 255.255.255.0
BSD
route add -net default 192.168.1.1 255.255.255.0
LINKS
Good description of routing concepts [9] by Damian James at Brismesh
[10]
Links:
------
[1] http://melbournewireless.org.au/#introduction
[2] http://melbournewireless.org.au/#configuring_ip_forwarding
[3] http://melbournewireless.org.au/#linux
[4] http://melbournewireless.org.au/#bsd_variants__including_mac_osx_
[5] http://melbournewireless.org.au/#windows_
[6] http://melbournewireless.org.au/#looking_at_the_routing_table
[7] http://melbournewireless.org.au/#default_route
[8] http://melbournewireless.org.au/#links
[9] http://home.pacific.net.au/~djames.hub/mesh/routing_faq.html
[10] http://www.itee.uq.edu.au/~mesh/index.html
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