Appendix B
:
Appendix B IP Addresses, Netmasks and Gateways
Communication between devices on a network running the Internet Protocol (often
abbreviated IP) is based each device on the network having an unique IP address. An IP
address is a 32-bit value divided into four "octets" of eight bits each. The 32-bit IP address is
commonly written with each of the four octets written as decimal numbers separated by
dots
1
.
For example: 192.168.0.40
One of the important features of the Internet protocol addressing scheme is its ability to
divide a network into "subnets" that share some portion of the 32-bit IP address for all
devices on the subnet. For example, all the devices on a small office or home network,
often share the same first three octets in their IP addresses. Only the last octet is different
for each device on such a network. Thus, all the devices on this type of network might have
192.168.0.xx as the first three octets and then each individual computer or device on the
network has an unique last octet. For example, a particular computer on this subnet might
have the IP address 192.168.0.40.
The part of the IP address that is common to all the devices on a particular subnet is called
the "network prefix", since that part of the address defines a unique subnet. The part of the
IP address that is unique to each individual device on the network is called the "host part".
In our first example, 192.168.0. is the "network prefix" while 40 is the "host part".
This scheme of dividing a network into subnets makes managing network traffic between
devices on a network much more efficient, since much of the traffic between computers and
other devices occurs within a subnet and does not affect devices on other subnets.
B.1
The Netmask Parameter
Every device on an IP network has a "netmask" parameter in addition to an IP address. The
netmask defines which portion of the IP address is a "network prefix" and which portion is a
"host part". Netmasks are written in the same notation (four octets separated by dots) as IP
addresses.
Zeros in a netmask value represent portions of the IP address that are the host part, while
1's in the netmask (expressed in binary notation) represent portions of the IP address that
are the network prefix.
In our example, the netmask for a subnet where all the devices share the first three octets
would be 255.255.255.0. The first three values are all 1's in binary, so the first three octets
are the network prefix. The last octet is zero, so all the bits of the last octet are the host part.
The following table shows several valid netmasks and the size (in bits) of the network
address portion and the host address portion of the IP address.
1
This appendix describes IPv4 addresses which are the most common on the Internet. A newer IPv6 standard, using 128 bit
addresses, instead of 32-bit addresses has been defined and is gradually supplanting the IPv4 scheme. However, most devices still
implement IPv4 and most computers running modern operating system versions support both. This appendix does not address IPv6. The
Instreamer ICE only supports currently IPv4.
Released: 7 Apr 2016
Instreamer ICE 50 User Manual
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