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| Appendix A
Gateway addresses often end with .1 or .254. This is not a requirement; they could end with any number between 1 and 254.
It is only a convenience because it leaves a continuous range of numbers that can be used by local hosts.
What about ending with .255 you ask? It is true that the largest possible value is 255 (or 11111111 in binary). But
addresses that end in all ones have a special meaning in the Internet Protocol. They are local broadcast addresses. A packet
sent to such a broadcast address (.255 on a class C network, .255.255 on a class B network, etc.) will be sent to all hosts on
the local subnet.
DNS
DNS stands for Domain Name System, and in some ways it is similar to how the telephone book works: if you
know the name, you can look up the corresponding phone number to dial. DNS servers allow IP devices to find
the IP address that corresponds to a given name (like telos-systems.com). The device can then use the IP address
to talk to the host that has the name. Without a DNS server you would not be able to use address names, only raw
numbers.
DHCP
The Dynamic Host Configuration Protocol (DHCP) is a method of handing out IP address to IP devices on a
network in a dynamic fashion. When an IP device that is configured to use DHCP is powered up (or connected to
the network), it broadcasts a request for IP configuration information on the subnet. If a DHCP server is available,
it will allocate an unused IP address from a user specified range and respond back to the device. The device can then
configure itself with this IP address.
Using DHCP is a convenient method to configure an IP device, but it is not always the best course of action. When you use
DHCP you don’t know the assigned IP address of the device, plus this address may change from time to time. This is usually
not a problem, but in some cases it can be. If you need to configure the Z/IP ONE via a web interface, you will have to check
the currently assigned IP address on the device via the front panel. Another situation where you do not want to use DHCP is if
you wish to configure port forwarding on your NAT (see below), since you must forward each desired port to specific internal
IP address.
Discover the Local Network Settings
You need to plug your Z/IP ONE into a network, but you don’t know the network settings. If there is no one to ask,
what can you do?
Well, if there is a PC already plugged into the same network, then you can check the network configuration on the
PC to determine the available network settings. The directions here are for a Windows PC.
1.
Press and hold the windows key, then press R to bring up the windows Run dialog box. Type “cmd”
(without quotes) in the dialog, and press enter.
You can also launch cmd from the start menu, but the steps to do this vary between versions of Windows.
