GE GFK-1541B - Manual (Page 186)

GFK-1541B Chapter 6 Network Administration Support 6-11
6
DDP Name Resolution
If local name table name resolution fails, DDP (a GE Fanuc naming protocol) is used to
dynamically resolve the symbolic name. DDP name resolution involves the client node
broadcasting a message on the network asking if any node recognizes the symbolic name. If a
node does recognize the name, it responds and supplies the associated IP address. The client can
then proceed with communication directly to that IP address. DDP uses broadcast traffic to
perform name resolution. Certain routing configurations do not support routing of broadcast
traffic, which implies that DDP name resolution will not work over such routers.
DNS Name Resolution
If both local name table and DDP name resolution fail, DNS is then attempted. This protocol is
an industry standard for resolving symbolic names to IP addresses with the assistance of a remote
DNS name server. The format of DNS usage is defined by RFCs 1034 and 1035. A separate
DNS name server on the network is required for DNS operation.
To use DNS name resolution, the IP address of the remote DNS name server must be supplied to
the Ethernet Interface in the PLC configuration. The symbolic name must be defined at the DNS
name server.
Name Usage
Various areas of the PLC system support the use of this naming architecture. They can be broken
into three categories: Channel API commands, Ethernet Global Data (EGD), and Station Manager
commands.
Some Channel API commands allow the use of symbolic names in the remote node addressing
fields of the COMMREQ Function Block.
In the configuration of an EGD exchange, the local Ethernet Interface that is responsible for
producing/consuming the EGD is identified by its network address name (adapter name). Also,
in the configuration of a produced exchange, the consumer address may be identified as a
symbolic name. For more information, refer to the chapter: “Ethernet Global Data”.
The following Station Manager commands pertain to symbolic names: MYNAME, NAMETBL,
BROWSEDDP
, PING, REM, and RESOLVE. These commands are described in detail in
GFK-1186, TCP/IP Ethernet Communications for the Series 90 PLC Station Manager Manual.