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6.2 TCP/IP Primer on IP Addresses
Obtaining IP addresses to interact over an existing, operating, network can involve a num-
ber of complications, and must usually be done with cooperation from your ISP and/or
network systems administrator. For this reason, it is suggested that the user begin instead
by using a direct connection between a PC and the RCM3209 board.
In order to set up this direct connection, the user will have to use a PC without networking,
or disconnect a PC from the corporate network, or install a second Ethernet adapter and set
up a separate private network attached to the second Ethernet adapter. Disconnecting your
PC from the corporate network may be easy or nearly impossible, depending on how it is
set up. If your PC boots from the network or is dependent on the network for some or all
of its disks, then it probably should not be disconnected. If a second Ethernet adapter is
used, be aware that Windows TCP/IP will send messages to one adapter or the other,
depending on the IP address and the binding order in Microsoft products. Thus you should
have different ranges of IP addresses on your private network from those used on the cor-
porate network. If both networks service the same IP address, then Windows may send a
packet intended for your private network to the corporate network. A similar situation will
take place if you use a dial-up line to send a packet to the Internet. Windows may try to
send it via the local Ethernet network if it is also valid for that network.
The following IP addresses are set aside for local networks and are not allowed on the
Internet: 10.0.0.0 to 10.255.255.255, 172.16.0.0 to 172.31.255.255, and 192.168.0.0 to
192.168.255.255.
The RCM3209 board uses a 10/100Base-T type of Ethernet connection, which is the most
common scheme. The RJ-45 connectors are similar to U.S. style telephone connectors, are
except larger and have 8 contacts.
An alternative to the direct connection is a connection using a hub. The hub relays packets
received on any port to all of the ports on the hub. Hubs are low in cost and are readily
available. The RCM3209 board uses 10/100 Mbps Ethernet, so the hub or Ethernet
adapter should be a 10/100 Mbps unit.
In a corporate setting where the Internet is brought in via a high-speed line, there are typi-
cally machines between the outside Internet and the internal network. These machines
include a combination of proxy servers and firewalls that filter and multiplex Internet traf-
fic. In the configuration below, the RCM3209 board could be given a fixed address so any
of the computers on the local network would be able to contact it. It may be possible to
configure the firewall or proxy server to allow hosts on the Internet to directly contact the
controller, but it would probably be easier to place the controller directly on the external
network outside of the firewall. This avoids some of the configuration complications by
sacrificing some security.
User's Manual
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