E: Alternative Ways to Assign an IP Address
XPress™ DR Industrial Device Server User Guide
91
E: 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.
Provided a DHCP server exists on the network, it will assign the unit an IP address, gateway
address, and subnet mask when the unit boots up. The XPress DR has acquired an IP address if
the red LED stops flashing and the green Status LED is on continuously. (If no DHCP server
exists, the unit responds with a diagnostic error: the red Diagnostic LED blinks continuously, and
the green Status LED blinks five times. This blinking only continues for about 15 seconds.)
You can use the Lantronix® DeviceInstaller™ software to search the network for the IP your unit
has been assigned by the DHCP server and add it to the managed list. See
Add the Unit to the
Manage List
later in this chapter.
Note:
This DHCP address will
not
appear in the unit’s standard configuration screens. You can
determine your unit’s DHCP-assigned IP address from the DHCP server, or in Monitor Mode.
When you enter Monitor Mode from the serial port with network connection enabled and issue the
NC
(Network Communication) command, you will 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 automatically obtain an IP address in
smaller networks that may not have a DHCP server. A range of IP addresses (from 169.254.0.1
to 169.254.255.254) has been explicitly reserved for AutoIP-enabled devices. The range of Auto
IP addresses is not to be used 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 itself. After reboot, the unit sends out another ARP request to see if
the selected address is in use, and so on.
AutoIP is not intended to replace DHCP. The unit will continue to look for a DHCP server on the
network. If a DHCP server is found, the unit will switch to the DHCP server-provided address and
reboot.
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.
An IP address is a 32-bit value, divided into four octets of eight bits each. The standard
representation is four decimal numbers (in the range of 0..255) divided by dots.
