Echelon IP-852 Channel - Manual (Page 50)

42 Using NAT, DHCP, DNS on an IP-852 Channel
channel outages due to IP address changes, use static addresses that do not
change.
Linking DNS and DHCP
DNS and DHCP are separate standards. A network can use DNS without using DHCP,
and vice versa. You can, however, link DNS and DHCP servers in a single network so
that all IP addresses on the network could be allocated dynamically, but still be
referenced by name. While this can work for private networks, usually within
corporations, it is not practical for the Internet.
If your IP-852 channel implementation is under your control, and you have control of all
DHCP and DNS servers referenced by the members of your IP-852 channel, you can
assign each device an IP address using DHCP without static reservations, and resolve
host names using DNS and the IP-852 Configuration Server. This section describes how
you can do so.
Note: The IP-852 Configuration Server requires a single static IP address for all
computers running LNS (version 3.0x or later) that are connected to an IP-852 channel.
If you leave the IP-852 Configuration Server attached to the IP-852 channel, DNS
resolvable addresses can be used. If the IP network links its DHCP server and DNS
server, then IP-852 devices can be setup to use DHCP assigned addresses. However, the
IP-852 Configuration Server’s ability to resolve addresses through DNS is limited.
Dynamic DNS (DDNS) can also be used with the same precautions. For more
information on DDNS, see the next section, Dynamic DNS.
The ISO/IEC 14908-4 standard requires that devices on an IP-852 channel share IP
addresses instead of DNS resolvable names. If an IP-852 device in a channel is aware of
a peer at 131.1.23.52, and that peer changes addresses, the IP-852 device will lose
communication with the peer until it receives an updated peer list. The IP-852
Configuration Server can solve this problem by sending out an updated list (using DNS)
to all members on the channel. The IP-852 device cannot resolve DNS address issues on
its own.
If DHCP will be used to retrieve the IP information for an IP-852 device, the network
administrator must ensure that a DHCP server is available to provide the IP address,
subnet mask, and gateway address.
Dynamic DNS
If your network administrator or ISP does not offer a static IP address service, you can
use a third party solution called dynamic DNS (DDNS). Providers include dns2go.com,
dyndns.org, and others. Perform a quick Internet search on “dynamic DNS”.
How DDNS Works
DDNS operators rely on the fact that your computer’s IP address does not frequently
change. Depending on your network administrator or ISP, the computer address may
change only when you power cycle your NAT gateway. If your NAT gateway is on 24/7, it
may be months before your computer’s address changes. It is also possible that your
network administrator or ISP forces the address to change even if the gateway is not
power cycled. The amount of time that a device may keep its address is called its “lease”.
DHCP servers lease an address for a period of time after which the lessee is required to
go back and acquire another lease.