If you have many different network segments on your local network, then you may wish to explore using the NETWORKS file, which provides network-name to address mapping capabilities. This file is similar to the services file in that it is not used really used by any applications other than for displaying information in a way that is easier for humans to understand. Applications which display segment-specific statistics for your network can leverage the entries stored in the NETWORKS file, displaying the networks by name instead of by number, which can make diagnosing your network easier.
The NETWORKS file is similar to the SERVICES file. There are three distinct columns, for the network name, the network number, and any aliases you may wish to have. Comments are defined through the use of "#" marks; anything after the "#" is considered to be a comment. Each platform varies in it's implementation, so refer to the documentation that came with your system to be sure of what's acceptable or not.
Figure C.3 below illustrates an example NETWORKS file.
# # "Net Name" "Net Number" "Aliases" "#Comments" # local 127 loopback Orlando 204.217.177 #Unoverica Orlando SanMateo 192.155.13.56 #Unoverica San Mateo
The network name can be whatever you want it to be. Since the only reason for using the NETWORKS file is to help you diagnose your network, these fields should be something that distinguishes that specific network segment. Names such as MKTG-UPSTAIRS or ENG- SANJOSE are good ones to use. In the example above, there are examples for Unoverica Corporation's networks in Orlando, Florida and in San Mateo, California. There is also an entry for the loopback network that comes as a part of the TCP/IP stack.
The network number can be in many different forms. It can be just the relevant octets of the network portion of the address, as in the "local" entry above. Since the loopback network address is always 127.0.0.1, and the 127 network is a Class A network, then the only relevant octet is "127". This entry could also have been mad using 127.0.0.0, which is the same as 127 alone.
Another example of this is the "Orlando" entry, which is a Class C network. Since the first three octets are significant on Class C networks, 204.217.177 is used in the entry. This entry could also have been made using 204.217.177.0, which would be the same thing (since "0" signifies that there are no subnets in use).
The "SanMateo" entry is on a sub-netted Class C network, so that entry shows the complete network number for that segment. This entry could also have been made using 192.155.13.0/ 255.255.255.248, which is the Class C network number followed by the appropriate subnet mask for that network.
For more information on the HOSTS database file, refer to section C.2.1 HOSTS. For more information on the SERVICES database file, refer to section C.2.2 SERVICES.
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