NAT (Network Address Translation) for BeOS
version 1.5.1
by Richard Burgess
rickb@spy.net / www.rickb.com
What Is it?
This net_server add-on allows your BeOS computer to serve as an Internet
router. Unlike the existing IP Forwarding network feature, NAT allows you
to use a single assigned IP Address to service all the machines
on your network. That means, for example, that you could connect over
a PPP connection and all the machines on your network
could access the Internet without the need to obtain addresses for
each one from your service provider. It is similiar to Linux's
IP-Masquerade and BSD's own NAT feature.
What it is not
NAT is NOT a proxy server. Don't configure your web browser or anything
else to use a proxy. NAT operates completely transparently.
Installing
With the current version of the BeOS (R4), you will need to put the nat add-on
in /boot/beos/system/add-ons/net_server. After doing this, open up the NATConfig
preferences app (I'd suggest making a link in your Preferences folder to it). In the Network
Interfaces box, you will need to set with network interface you will use for your LAN and
which will be your Internet interface. If you have not already configured your Ethernet and/or
modem, you'll need to do this first before you can configure NAT. After selecting the interfaces,
click the NAT on checkbox and hit restart networking. NAT is now configured! See the sections
below on how to tweak the advanced settings and use static port mapping.
NOTE: NAT automatically turns on IP forwarding and requires this feature to operate, so be sure
to leave it checked in the Network preferences.
Setting up your LAN
After configuring your machine you will now need to set up the machines on your
LAN to use it as the default gateway. Consult the
appropriate documentation for those systems
on how to do this. You will also need to assign IP addresses from the "unroutable"
blocks assigned for this purpose. The class C blocks are
192.168.0.x - 192.168.255.x. Your NAT machine should also use one of these addresses (that will be your gateway IP)
Advanced Settings
There are additional configuration options that you
can tweak if you want. Defaults that NAT uses are
shown parentheses.
START_PORT (30000) Start of ports that NAT will use for address mapping
END_PORT (60000) End of ports that NAT will use for address mapping
PORT_TIMEOUT (4) Time (in minutes) that a port used for mapping will time out
SOCKET_TIMEOUT (1) Time (in minutes) after which sockets reserved for NAT but
unused will be reclaimed by the system
SOCKET_POOL_SIZE (5) The size of the pool of sockets reserved and ready for use.
Static Port Mapping
Static Port Mapping allows you map certain ports on your NAT machine to ports on other machines on
your LAN. This allows you to run things like web servers, etc, from other machines through your NAT box.
Currently Tested and Supported Protocols/Apps
HTTP, POP, SMTP, NNTP, telnet, FTP in passive mode
and probably others.
The main criteria is if the protocol uses
port numbers and ip addresses outside the TCP/IP headers then it probably won't work.
Definitely not Supported
ping (ICMP), FTP in active mode
Source code is available on request. If you are interested in adding support for more protocols let me know as I have provided a simple API to allow support for protocols that require additional translation.
Version history
1.5.1
Fixed bug where the config app wouldn't add its settings if there wasn't already a nat section in the network file.
1.5
GUI interface
Static Port Mapping
Fixed bug where only UDP sockets were being created.
Now looks for FIN flag in TCP packets so we can reclaim the port immediately when a connection closes.
Now waits for threads to die in destructor. This should make net restarts a bit more stable.
1.0 Initial release
And a big thanks to Olaf Seibert for his very thorough testing and great suggestions.