Motion Coordinator Technical Reference Manual
Communications Protocols 13-27
Ethernet
The beginning Network Address portion of 192 begins with the first three bits as
110... and classifies it as a Class C address. This means you can have up to 256
host addresses on this particular network.
If you wanted to add sub-netting to this address, then some portion (in this
example, eight bits) of the host address could be used for a subnet address.
Thus:
<-Network address->.<-Subnet address->.<-Host address->
192.168 . 000 . 250
To simplify this explanation, the subnet has been divided into a neat eight bits
but an organization could choose some other scheme using only part of the third
quad or even part of the fourth quad.
A subnet (short for "sub-network") is an identifiably separate part of an organiza-
tion's network. Typically, a subnet may represent all the machines at one geo-
graphic location, in one building, or on the same local area network (LAN).
Having an organization's network divided into subnets allows it to be connected
to the Internet with a single shared network address. Without subnets, an organ-
ization could get multiple connections to the Internet, one for each of its physi-
cally separate sub-networks, but this would require an unnecessary use of the
limited number of network numbers the Internet has to assign. It would also
require that Internet routing tables on gateways outside the organization would
need to know about and have to manage routing that could and should be han-
dled within an organization.
The Subnet Mask
Once a packet has arrived at an organization's gateway or connection point with
its unique network number, it can be routed within the organization's internal
gateways using the subnet number as well. The router knows which bits to look
at (and which not to look at) by looking at a subnet mask. A mask is simply a
screen of numbers that tells you which numbers to look at underneath. In a
binary mask, a "1" over a number says "Look at the number underneath"; a "0"
says "Don't look." Using a mask saves the router having to handle the entire 32-bit
address; it can simply look at the bits selected by the mask.
Using the Trio default IP address, the combined network number and subnet
number occupy 24 bits or three of the quads. The default subnet mask carried
along with the packet is:
255.255.255.000
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