User Manual

Section 2: Advanced Topics
DHCP
DHCP (Dynamic Host Configuration Protocol) allows PCs to automatically be assigned
an IP address when they are powered. The “DHCP Server” resides on the network and
assigns IP addresses. When you select “Obtain IP address Automatically” in the
Windows network setup screens, you are asking Windows to get its IP address from a
local DHCP server. DHCP is commonly used for workstations, but seldom used for
servers. For example, your company’s web server likely has a static IP address instead of
a DHCP assigned address.
DHCP addresses are assigned in the order computers are powered on. Computer 1 is
assigned address 100, computer 2 is assigned address 101, computer 3 is assigned address
102, etc. If computers are powered down and then later restarted, there is no guarantee
that they will receive the same address. This is a problem if you want to setup a
communication channel between a set of computers (as is done when creating a
L
ONWORKS/IP channel). In a LONWORKS/IP channel, each device knows the addresses
of other devices on the network. If those addresses change because a peer running as a
DHCP client was power cycled, then all members of the group need to be updated with
the new IP address. This is easily accomplished by updating an entry in the Configuration
Server, but the process is manual, which makes it impractical.
Note: Echelon recommends that all members of a L
ONWORKS/IP channel be assigned
static IP addresses.
If you are in control of your DHCP server, you may be able to configure your DHCP
server to always assign your i.LONs the same address. This is called making a static
reservation, and is supported by most DHCP servers. Using DHCP with static
reservations is acceptable and is similar to using static IP addresses. If you decide to use
this technique, each i.LON should be instructed to acquire its IP address from the DHCP
server by selecting Automatically obtain IP address in the main TCP/IP Web setup
screen.
Figure 31. Automatically obtain IP address Setting
48 Using the i.LON 600 with DHCP & DNS