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xDirect User Guide 77
Appendix D: Alternative Ways to Assign an IP
Address
Earlier chapters describe how to assign a static IP address using DeviceInstaller, Web Manager,
and Setup Mode (through a Telnet or serial connection). This section covers other methods for
assigning an IP address over the network.
DHCP
The unit ships with a default IP address of 0.0.0.0, which automatically enables DHCP. If a DHCP
server exists on the network, it provides the unit with an IP address, gateway address, and subnet
mask when the unit boots up.
You can use the DeviceInstaller software to search the network for the DHCP-assigned IP address
and add it to the list of devices retrieved.
Note: This DHCP address does not appear in the unit’s Setup Mode or in Web
Manager. You can determine your unit’s DHCP-assigned IP address in Monitor Mode.
When you enter Monitor Mode from the serial port with network connection enabled and
issue the NC (Network Communication) command, you see the unit’s IP configuration.
AutoIP
The unit ships with a default IP address of 0.0.0.0, which automatically enables
Auto IP within the unit. AutoIP is an alternative to DHCP that allows hosts to obtain an IP address
automatically in smaller networks that may not have a DHCP server. A range of IP addresses
(from 169.254.0.1 to 169.254.255.1) has been explicitly reserved for AutoIP-enabled devices. Do
not use this range of Auto IP addresses over the Internet.
If your unit cannot find a DHCP server, and you have not manually assigned an IP address to
it, the unit automatically selects an address from the AutoIP reserved range. Then, your unit
sends out a (ARP) request to other nodes on the same network to see whether the selected
address is being used.
If the selected address is not in use, then the unit uses it for local subnet communication.
If another device is using the selected IP address, the unit selects another address from the
AutoIP range and reboots. After reboot, the unit sends out another ARP request to see if the
selected address is in use, and so on.
AutoIP does not replace DHCP. The unit continues to look for a DHCP server on the network. If it
finds a DHCP server, the unit switches to the DHCP server-provided address and reboots.
Note: If a DHCP server is found, but it denies the request for an IP address, the unit
does not attach to the network, but waits and retries.
AutoIP can be disabled by setting the unit’s IP address to 0.0.1.0. This setting enables DHCP but
disables AutoIP.